Chapter 4 Rocks and Minerals

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Rocks Lesson #10

Rock Lesson - Title

 

Welcome to the lesson "Rocks".

 

The Earth was formed about 4.6 billion years ago. The planet was so hot that the entire Earth was molten or liquid. As the Earth cooled, the lightest materials floated to the top and the heaviest materials sank to the center. The outer part of the Earth, the crust, consists of the lightest rock.

 

Rock Lesson - lava flow 

The lightest rocks form the continents, which are made mostly of the rock granite. Most of the granite on the continents has, over millions of years, been broken down, transported, and deposited into sedimentary rock. These layers of sedimentary rock vary from 8-9 miles thick to nothing in some areas like the Canadian Shield of North America. The Canadian Shield has huge outcroppings of granite right on the surface. Under the thick layers of sedimentary rock lies the denser granite. 

 

The granitic continents ride on a much denser rock called basalt. These basalts form the bottom of our continents and the bottoms of our great oceans. This layer of rock extends down to 40 miles from the surface of the earth. 

 

Rock Lesson - Lithosphere 

The crust is very thin in comparison to the other layers of the earth. The crust is only 3 miles thick under the oceans and about 40 miles thick under the highest mountain chains. The layer of the earth under the crust is called the mantle. It is over 1800 miles thick!! The crust and the upper level of the mantle form a layer of the earth that moves very slowly (1-4 inches per year). This layer that moves and causes earthquakes and volcanoes is called the Lithosphere.

 

Rocks are made of two or more different minerals that have been:

1. cemented together, or

2. squeezed and heated together, or

3. melted and cooled together.

 

Rocks make up the majority of the Earth's crust. One of the most common rock is granite. The four minerals that make up granite are feldspar, quartz, mica, and hornblende. Granite was formed when magma cooled slowly forming crystals of the four minerals that make up the rock granite. 

 

Rock Lesson - Granite 1

Look at the photo above of granite. Notice the different mineral crystals that make up the rock, granite.

 

Most of the Earth's surface rocks are covered by soil or clay. Soil contains very small crushed pieces of rock and organic (plant and animal remains) material. Plants such as grass and trees grow in this region of the crust.

 

Rock Lesson - Hawaii photo

The photo above shows a recent eruption of ash that has covered and burned an area of dense vegetation in Hawaii. The lava has cooled and is now a volcanic rock called basalt. The weathering process will break the basalt down into small, finer pieces of rock called soil. This process can take a few years or thousands of years to produce soil fine enough for plants to grow well in. The soil will become fertile when bacteria decomposes plant and animal material adding nutrients for living plants. 

Rocks are produced in a variety of ways and have been cycled in some area many times. This cycling of the rocks is called the rock cycle.

 

Rock Lesson - Rock cycle 

The rock cycle shows how the earth's rocks are changed again and again. The rocks can be changed at times to another type of rock. The rock cycle can begin anywhere in the cycle. Lets start with igneous rocks. Igneous rocks start as magma. The magma (molten rock under the surface) and lava (molten rock on the surface) hardens into igneous rock. The igneous rock then breaks apart over time through the process of weathering. These bits of broken rock are washed away by rains and deposited in a river. These pieces of igneous rocks are cemented together with other bits of rock and form a sedimentary rock called conglomerate. Over time sedimentary rocks can be buried by earthquakes or other geologic processes. Being buried deep under the surface in areas of high temperatures and pressures or coming in contact with magma can cause these sedimentary rocks to change to metamorphic rocks. 

 

Rock Lesson - Diagram 

Diagram 1 shows layers of rocks around and under a volcano. The white blocks are a sedimentary rock called limestone. Limestone forms on the bottom of the ocean over many, many years. The fish and shelled sea animals decompose and their bones and shells break down into a chemical called calcium carbonate (CaCO3). This is the cementing agent that binds the sediments that fall to the sea floor into the rock called limestone. Magma has pushed its way to the surface and is now coming into contact with the surrounding rock layers. 

Diagram 2 shows the limestone being heated by the magma and changing to the metamorphic rock called marble (Yellow). Marble is a beautiful rock that is used by humans as building material and for decorative uses as in sink tops or monuments. Artists have sculpted marble into some of the greatest works of art in the world.

 

Rock Lesson - Rock Classification

The three main rock classifications are Igneous, Sedimentary, and Metamorphic. Rocks are classified into these groups by the way they were formed. 

Rocks that formed from magma are called igneous rocks. Igneous comes from the Latin word ignis which means "fire". Rocks that are formed from heat and pressure are called metamorphic rocks. Rocks that are formed from the cementing together of small pieces of rocks or shells are called sedimentary rocks. We will discuss these three types of rocks more in depth later in this chapter.

 

Rock Lesson - US Map 

This map of the United States and parts of Mexico and Canada shows what type of rock makes up the surface of these regions. The majority of the surface rocks on the North American continent are sedimentary. The mountainous regions of the west and southwest are made of igneous rocks. The Appalachian Mountain region of the eastern U.S. and most of eastern Canada are made of metamorphic rocks.

 

Rock Lesson - Granite 

Granite is an igneous rock that is composed of four minerals. These minerals are quartz, feldspar, mica, and usually hornblende. Granite forms as magma cools far under the earth's surface. Because it hardens deep underground it cools very slowly. This allows crystals of the four minerals to grow large enough to be easily seen by the naked eye. Look at the photo of granite above, notice the different crystals in the rock. 

Granite is an excellent material for building bridges and buildings because it can withstand thousands of pounds of pressure. It is also used for monuments because it weathers slowly. Engravings in the granite can be read for hundreds of years, making the rock more valuable. 

Granite is quarried in many places in the world including the United States. The state of New Hampshire has the nickname "Granite State" because of the amount of granite in the mountains of that beautiful state. The Canadian Shield of North America contains huge outcroppings (surface rocks) of granite.

 

Rock Lesson - Milky Quartz

Milky quartz is a common mineral that is found in many different types of rocks. The chemical formula is Silicon oxide (SiO2). One type of quartz is easily identified by its hexagonal crystals, but quartz can also be found in a large mass. Quartz can be broken or weathered into the tiny pieces we know as sand. Quartz is a very hard mineral and in fact is the hardest of the common minerals. Quartz is number seven on the Mohs hardness scale. Quartz is also chemically stable, which means that it weathers very slowly.

 

Quartz can be colored yellow, milky white, rose, smoky (brown or black), and the best known of the colored crystals amethyst, which is purple. Impurities in the rock at the time of formation causes the quartz crystal to have these different colors. 

Quartz is used by humans in producing optical instruments and electical devices. It is also used to make sandpaper and grinding tools.

 

Rock Lesson - Pink Feldspar

Feldspar is the most abundant mineral in rocks that are located at or near the earth's surface. Feldspar can have a glassy white, blue, green, or red crystals. All feldspars contain silica and aluminum. 

When feldspars are exposed to the atmosphere they break down or weather easily. When they are broken down, feldspar forms other minerals, many of which are clay minerals. Feldspars also contain potassium which is a major nutrient for plant growth. 

The clays formed by weathered feldspar are used by pottery manufacturing plants. Kaolinite is the highest quality of the feldspar clays used by potters. 

Feldspar is number 6 on the Mohs hardness scale.

 

Rock Lesson - Hornblende

Hornblende is a mineral that contains magnesium, iron, silica and aluminum. Hornblende is black, brown and green in color. It occurs in crystals of many igneous rocks.

 

Rock Lesson - Biotite Mica

Mica is a mineral that can be split into very thin sheets. These sheets can be so thin that 1000 can be layered into mica 1 inch high. Mica can be clear, black, green, red, yellow, and brown. Clear mica is called Muscovite because it is found near Moscow, Russia and was used as window glass in the Muscovite's homes. Muscovite contains water which helps to make it clear. Biotite mica is dark green to black in color because it contains iron, magnesium. 

Mica is mined in Brazil, India, many parts of Africa, Canada, and the United States. It is used in the manufacturing of electronic and electrical devices.

 

Write the answers to the following questions in complete sentences on a piece of paper.

 

In your own words write a definition for rock. 


What is soil composed of? 


Describe in your own words how the rock cycle works. 


Name the four minerals that granite is made from and a human use for each of the four minerals. 


Name the three classifications for rocks.

 

 

 

 

 

Minerals Lesson #11

Welcome to the lesson "Minerals".

 

A mineral is a solid material, made of one substance, that occurs naturally on Earth. Most of the common minerals are made of crystals. A Crystal is a solid formed by a repeating, three-dimensional pattern of atoms, ions, or molecules and having fixed distances between the different parts. Minerals that do not grow in these regular or crystalline patterns are called Amorphous solids.

 

Some minerals can be both crystalline and amorphous. The two photos above show a crystalline quartz specimen and an amorphous quartz specimen.

 

Quartz is a mineral made from one substance SiO2 (Silicon Oxide) that has a definite chemical composition. The quartz that you find in Asia has the same basic chemical make up as quartz found in Minnesota.

 

 

There are 92 naturally occurring elements on earth but only eight elements make over 98% of the minerals on the Earth's crust. They are, in decreasing quantity, 1 oxygen, 2 silicon, 3 aluminum, 4 iron, 5 calcium, 6 sodium, 7 potassium, 8 magnesium. The graph above shows you the amounts of these elements in the Earth's crust.

 

There are over 2000 minerals on Earth, but only 100 are commonly found. 30 minerals make up the majority of the rocks on Earth. You will be studying these minerals in this series of lessons. Rocks, as you learned in the last lesson, are made of two or more of these minerals.

 

 

There is a great difference in the way different minerals look. Some minerals sparkle in the light while others are dull and boring!! Some minerals are so hard that they can scratch steel while other minerals are so soft that they feel powdery and can be scratched easily by a fingernail. There are many ways that scientists classify or group minerals, in this lesson we are going to study five properties. A property is a characteristic of a mineral. Properties help scientists to better understand how the mineral was formed and also to help identify a mineral. The five properties that we are going to study are luster, hardness, cleavage and fracture, color and streak, and magnetism.

 

Luster is a property of a mineral that tells how the mineral reflects light. Luster gives you an indication of how "Shiny" a mineral is. The two main ways that geologists categorize a mineral's luster is Metallic and Non-metallic. The luster of a mineral may differ from sample to sample. Metallic minerals shine like metal, while non-metallic minerals vary greatly in their appearance. There are many different descriptions of non-metallic luster, we are going to discuss four. They are pearly, earthy, vitreous (glassy), and greasy. Pearly luster is iridescent, glows like a pearl. Greasy luster looks like the mineral is covered with grease, the mineral definitely shines. Minerals with an earthy luster have a dull look with no shine. Minerals with an earthy luster look as though they are covered with dirt or dust. The photos above shows examples of these four lusters. Minerals with a vitreous luster (glassy) look like small pieces of a broken glass bottle

 

 

Color is the easiest of the properties to see, but it is not always the best way to identify a mineral. Many minerals have more than one color because of impurities that were present during the formation of the mineral. Quartz is an example of a mineral with many different colors. Quartz can be clear, white, blue, brown, and almost black. Amethyst is a quartz crystal with a purple color. The impurity that makes amethyst purple is manganese.

A better determinant of the true color of a mineral is its streak. Streak is a test used by a geologist to see the color of the mineral under the top layer or coating on the mineral. The mineral is rubbed on a "streak plate", which is a piece of porcelain. When the mineral is rubbed across the streak plate some of the mineral is broken off and ground into a powder. This allows the geologist to see under the outer layer which could have a different color due to the mineral being exposed to the atmosphere. When minerals are exposed to the atmosphere, gasses like oxygen can chemically combine with the mineral to change its outer color.

The photo above is showing a specimen of iron pyrite along with a streak plate showing the pyrite's streak.

 

 

In 1822 a German scientist by the name of Frederick Mohs set up a scale to determine the approximate hardness of minerals. (SEE CHART ABOVE!!!) He arranged the minerals in his scale from softest (Talc) to hardest (Diamond). The minerals get increasingly harder as you read down the scale, but they do not increase in hardness at a constant rate. Example: Calcite is not twice as hard as talc and a diamond is not 10 times harder than talc. In fact a diamond is over 40 times harder than talc. The line graph above shows you this relationship.

 

This property like color is arbitrary because the hardness of a mineral varies slightly from one specimen to the next. We can determine the approximate hardness of a mineral by running a group of tests. Scratch the mineral in question with a fingernail, penny, iron nail, or glass slide. If the mineral shows a scratch mark from one of the testing materials the mineral is said to be less hard than the mineral that scratched it. Example: A piece of pink feldspar will not be scratched by a fingernail, penny, or an iron nail, but will be scratched by a glass slide. The feldspar is said to be harder than the first three testing materials but not as hard as the glass slide.

 

You can use the following materials to run your own mineral hardness tests. 1) bar soap 2) fingernail 3) penny 4) easy to scratch knife blade 5) hard to scratch a knife blade 6) will scratch glass slide 7) quartz crystal.

 

 

Some minerals have a tendency to split or crack along parallel or flat planes. This property is easily seen in some minerals and you can test the mineral by breaking it with a hammer or splitting off sheets with a pen knife. These planes along which the mineral breaks are called cleavage planes. If the mineral splits easily along these planes the mineral is then said to have perfect cleavage. Mica is a good example of perfect cleavage. Feldspar is an example of a mineral with cleavage in more than one direction. Quartz is a mineral that has no cleavage at all. Quartz shatters likes glass when struck with a hammer. The biotite mica on the far left splits into sheets that are perfectly parallel. They form because of weak and strong bonds between the mica layers. The feldspar breaks into two planes at consistent angles.

 

Fracture is related to cleavage. Fracture occurs when a mineral breaks at random lines instead of at consistent cleavage planes. Many minerals that have no cleavage or poor cleavage fracture easily. The obsidian on the far right is a good example of a rock that has conchodial (glass like) fracture. Quartz is a mineral that also has conchodial fracture.

 

 

Only two minerals on earth are magnetic. They both have high quantities of iron. Magnetite is one of the magnetic minerals and pyrrhotite is the other. Magnetite was used by ancient sailors for compasses. They would chip off needles of magnetite and float them on water and watch the needle point to the north.

The photo above shows small pieces of metal fillings magnetically attached to magnetite! The rock is a natural magnet!

 

 

Calcite is pure calcium carbonate (CaCO3). It is found in limestone and marble. It is the cementing agent that binds sediments together into sedimentary rocks. Marble is metamorphosed (changed by heat and pressure) limestone. The crystals formed from pure calcite are in the form of a perfect rhomboid. A rhomboid is a six-sided solid object in which the opposite sides are parallel. It has perfect cleavage in three directions. If you hit calcite with a hammer it will break into smaller but perfectly shaped rhomboids. Calcite is number two on Mohs hardness scale. Calcite is the material that forms stalactites and stalagmites in caves.

 

Calcite is used as a fertilizer, cement, chalk, building stone, and for the manufacture of optical instruments.

 

 

Talc is a mineral that has perfect cleavage and a greasy or soapy feel. It is given the distinction of being number 1 on Mohs hardness scale. Talc is also called soapstone which is used by artists for sculptures. Talc can be ground up into talcum powder. Ground talc is also used to make crayons, paint, paper, and soap. Talc is quarried in many Northeastern states of the United States.

 

 

 

Hematite is the most important source of iron ore in the world. The production of iron has been important to nations of the world for over 2500 years. Today the addition of other minerals to iron has lead to the production of steel which is vital to the economy of the major countries on Earth. Hematite has a red or black color but the streak is always red. The iron in the hematite turns red when it comes in contact with water and oxygen. In other words this rock is rusted!!

 

Hematite has a metallic or earthy luster. The hardness of hematite is about 5 on Mohs hardness scale. It has no cleavage and breaks with an uneven fracture. The reddish landscape of Mars is due to the oxidized iron on its surface. This tells us that water and oxygen must have been present on Mars at one time.

Hematite is mined in the Lake Superior and Appalachian mountain regions of the United States. Small deposits are found in many states of the union. Canada and Russia are leading countries in the mining of iron ore.

 

 

Magnetite is a mineral that has a very high iron content. Magnetite has a black or brownish-red color and a black streak. It has a hardness of about 6 on the Mohs hardness scale. It is one of two minerals in the world that is naturally magnetic. Magnetite, also known as lodestone, is found throughout the United States.

 

Magnetite is an important source of iron ore and occurs in many igneous rocks.

 

There is a city in Russia by the name of Magnitogorsk that received its name because of the unusually high quantities and quality of magnetite found in the mountains surrounding the city. Magnitogorsk is a leading iron manufacturing center in Russia today.

 

 

Galena is an important source of lead. Galena's chemical symbol is PbS, which is lead and sulfur. Galena may also contain silver. The United States is the leading producer of lead in the world. Lead was used in pencils and paint until it was found to be poisonous to humans . Today pencil "lead" is made of another mineral called graphite. Lead is used for fishing weights.

 

Galena is an iron sulfide and the main source of lead. Galena usually occurs in cubic crystals. If you hit a specimen of galena with a hammer it will shatter into small perfect cubic crystals. It has a metallic luster and a black to dark gray color and streak. Galena has a hardness of about 2.5 on Mohs hardness scale which is about as hard as your finger nail.

Galena is mined in Missouri, Idaho, Utah, Oklahoma, Colorado, British Columbia of Canada, and Mexico.

 

 

Write the answers to the following questions in complete sentences on a piece of paper.

 

1.

What is a mineral?

2.

What are physical properties of minerals?

3.

What eight elements make up over 98% of the Earth's crust?

4.

Write a pararaph describing the properties and human uses for one of the minerals that you studied in this lesson.

 

Igneous Rocks Lesson #12

Welcome to the lesson "Igneous Rocks".

 

When most people think about igneous rocks they envision a volcano erupting pumice and lava. The term igneous comes to us from the Latin word "Ignis" which means fire. Igneous rocks are produced this way but most igneous rocks are produced deep underground by the cooling and hardening of magma. Magma is molten (melted) rock under the surface of the Earth. It is produced in the upper reaches of the mantle or in the lowest areas of the crust usually at a depth of 50 to 200 kilometers.

The diagram above shows you where magma is produced at a subduction zone. Magma is less dense than the surrounding rock which causes it to rise. When magma reaches the surface it is then called lava and the eruptions of lava and ash produce volcanoes. The lava that reaches the Earth's surface will harden and become igneous rock. When the magma does not reach the surface it produces a variety of geologic structures. When lava reaches the surface of the Earth through volcanoes or through great fissures the rocks that are formed from the lava cooling and hardening are called extrusive igneous rocks. Some of the more common types of extrusive igneous rocks are lava rocks, cinders, pumice, obsidian, and volcanic ash and dust.

 

This is the volcano Paricutin that is located in Mexico. It is erupting cinders and pumice which are examples of extrusive igneous rocks.

 

Millions and even billions of years ago molten rock was cooling and thus hardening into igneous rocks deep under the surface of the Earth. These rocks are now visible because mountain building has thrust them upward and erosion has removed the softer rocks exposing the much harder igneous rocks. These are called intrusive igneous rocks because the magma has intruded into pre-exiting rock layers. Types of intrusive igneous rocks are granite and basalt.

The diagram above shows you a large intrusive igneous body called a batholith. A batholith is the largest of the intrusive bodies. They are larger than 100 square kilometers and usually form granite cores.

 

As you can see in the diagram above a batholith is a very large intrusive igneous body. There are two types of intrusive bodies that we are going to discuss 1)Discordant and 2) Concordant. A discordant igneous rock body cuts across the pre-exiting rock bed. Batholiths and dikes are examples of discordant rock bodies. A dike is a vertical or near vertical intrusive igneous rock body that cuts across rock beds. They frequently form from explosive eruptions that crack the area around a volcano with the magma filling the cracks forming a dike.

A concordant igneous rock body runs parallel to the pre-existing bedrock. Laccoliths and sills are examples of concordant igneous rock bodies. A laccolith is a dome shaped intrusive body that has intruded between layers of sedimentary rock. The rising magma forces the overlying layers to rise up into a dome. A sill is similar to a dike with the exception that sills run parallel to the existing rock bed instead of cutting through it.

 

The composition of igneous rocks falls into four main categories. They are determined by the amount of silica that the rocks contain. The four categories are acidic, intermediate, basic, and ultramafic. Acidic rocks have a high silica content (65% or more) along with a relatively high amount of sodium and potassium. These rocks are composed of the minerals quartz and feldspar. Rhyolite and granite are the two most common types of acidic rock.

Intermediate rocks contain between 53% and 65% silica. They also contain potassium and plagioclase feldspar with a small amount of quartz. Diorite and Andesite are the two most common types of intermediate rock.

 

Basic rocks are composed of less than 52% silica and a large amount of plagioclase feldspar and very rarely quartz. The two most common types of basic rocks are basalts and gabbros.

Ultrabasic rocks are composed of less than 45% silica and contain no quartz or feldspar. They are composed mainly of the minerals olivine and pyroxene. The most common ultrabasic rock is periodite. Periodite is a dark green, coarse-grained igneous rock that many scientists believe is the main rock of the mantle.

 

Basalts are dark colored, fine-grained extrusive rock. The mineral grains are so fine that they are impossible to distinguish with the naked eye or even a magnifying glass. They are the most widespread of all the igneous rocks. Most basalts are volcanic in origin and were formed by the rapid cooling and hardening of the lava flows. Some basalts are intrusive having cooled inside the Earth's interior.

 

This is a vertical columnar basalt formation. When basaltic lava cools it often forms hexagonal (six sided) columns. Some famous examples of columnar basalt formations are the Columbia Plateau overlooking the Columbia River near Portland, the Giant's Causeway in Northern Ireland, and the Devils Postpile National Monument in California (Above).

 

Pumice is a very light colored, frothy volcanic rock. Pumice is formed from lava that is full of gas. The lava is ejected and shot through the air during an eruption. As the lava hurtles through the air it cools and the gases escape leaving the rock full of holes.

Pumice is so light that it actually floats on water. Huge pumice blocks have been seen floating on the ocean after large eruptions. Some lava blocks are large enough to carry small animals.

Pumice is ground up and used today in soaps, abrasive cleansers, and also in polishes.

 

Rhyolite is very closely related to granite. The difference is rhyolite has much finer crystals. These crystals are so small that they can not be seen by the naked eye. Rhyolite is an extrusive igneous rock having cooled much more rapidly than granite giving it a glassy appearance. The minerals that make up rhyolite are quartz, feldspar, mica, and hornblende.

 

Gabbros are dark-colored, coarse-grained intrusive igneous rocks. They are very similar to basalts in their mineral composition. They are composed mostly of the mineral plagioclase feldspar with smaller amounts of pyroxene and olivine.

 

Obsidian is a very shiny natural volcanic glass. When obsidian breaks it fractures with a distinct conchoidal fracture. Notice in the photo to the left how it fractures. Obsidian is produced when lava cools very quickly. The lava cools so quickly that no crystals can form.

When people make glass they melt silica rocks like sand and quartz then cool it rapidly by placing it in water. Obsidian is produced in nature in a similar way.

Obsidian is usually black or a very dark green, but it can also be found in an almost clear form.

Ancient people throughout the world have used obsidian for arrowheads, knives, spearheads, and cutting tools of all kinds. Today obsidian is used as a scalpel by doctors in very sensitive eye operations.

 

Write the answers to the following questions in complete sentences on a piece of paper.

 

1.

In your own words write a definition for magma and lava.

2.

What is the difference between intrusive and extrusive igneous rocks?

3.

What are the most common extrusive and intrusive igneous rocks?

4.

What is the difference between granite and rhyolite and how are they similar?

 

Sedimentary Rocks Lesson #13

Welcome to the lesson "Sedimentary Rocks".

 

The land around you, no matter where you live, is made of rock. If you live in a place that has good rich soil, the soil itself is finely broken down or weathered rock.

People that live in a desert region can easily find rocks on the surface. These rocks lay on a surface of clay that is also a product of weathering rock. Weathering is the process of breaking down rocks and minerals into smaller pieces by water, wind, and ice.

Sedimentary rocks are formed from the breaking apart of other rocks (igneous, metamorphic, or sedimentary rocks) and the cementation, compaction and recrystallization of these broken pieces of rock.

The photo at the left shows layers of lava and ash in Hawaii that will, over time, and with the help of bacteria, break down into fertile soil.

 

Sedimentary rocks are formed from broken pieces of rocks. These broken pieces of rock are called sediments. The word "Sedimentary" comes from the root word "Sediment".

Sedimentary rocks are usually formed in water. Streams and rivers carry sediments in their current. When the current slows around a bend or the river empties into a lake, or ocean, or another river the sediments fall out because of gravity. The larger sediments fall out first and the lightest sediments fall out last.

The diagram above shows layers of sediment that were laid down in a lake. In the spring the lake receives an influx of water from the mountain snow melt. This snow melt carries with it a large amount of sediment that becomes suspended in the lake water. As the sediment settles out during the summer and especially in the winter, if the lake becomes frozen over, the sediments come to rest on the bottom. The heaviest and largest particles settle out first and the lightest sediments such as silts and clays settle out last. The number 1 shows sediment that would have been laid down during 1994, number 2 in 1995, and number 3 would have been laid down in 1996. The gray area above the 3 would be the latest layer being laid down at the present time. This laying down of rock-forming material by a natural agent is called deposition. Natural agents of deposition are water, ice, gravity, and wind.

Sediment is deposited in flat, horizontal layers with the oldest layers on the bottom and the younger layers laying on and over the older layers. Geologists use this knowledge to read layers of sedimentary rock like the pages in a book. They can date layers by the fossils that are found in them. If a layer has a fossil in it that is known to be 50 million years old the layer itself must be at least 50 million years old and the layers below it have to be older than 50 million years.

 

The size of sediment is defined by the size of the particles that make up the sediment. The largest sediment size is called a boulder. Boulders have a diameter that is larger than 256 millimeters (about 10 inches). Cobbles are the next largest sediment, they are 64 - 256 mm in diameter (about 3-10 inches). Pebbles are next in size and are 4-64 mm in diameter (about 1/6-3 inches). The next sizes of sediments are very small, granules are 2-4 mm, sand 1/16-2mm, silt 1/256-1/16 mm, and the smallest sediment size is clay which is less than 1/256 of a millimeter in diameter.

Sedimentary rocks are formed in three ways from these different sized sediments.

 

A sedimentary rock is a layered rock that is formed from the compaction, cementation, and the recrystallization of sediments.

Compaction is the squeezing together of layers of sediment due to the great weight of overlying layers of rock. This squeezing of the layer results in reducing the thickness of the original layer. When the layers are reduced in thickness the pore spaces around the sediments are also reduced, which leads to a tighter packing of the layers.

Cementation is the changing of sediment into rock by filling spaces around the sediments with chemical precipitates of minerals. binding the sediments, and forming solid rock. Calcite and silica are common minerals that cement the sediments together.

Recrystallization is the third way that sedimentary rocks are formed. Recrystallization is the formation of new mineral grains that are larger than the original grains. As the sediments recrystallize they arrange themselves in a series of interlocking crystals that connect the other grains together into a solid rock.

The photo to your left shows layers of sedimentary rocks that were deposited in flat horizontal layers. These layers were then uplifted and bent by mountain building.

 

Sedimentary rocks form a thin layer of rock over 75 per cent of the Earth's surface. They are the site of very important resources such as ground water, coal, oil, and soil. Shale, sandstone, and limestone are the most common types of sedimentary rocks. They are formed by the most common mineral that is found on or near the surface of the Earth. The mineral that forms these sedimentary rocks is feldspar.

Running water, such as the mountain stream above, sorts and transports more sediment than any other agent of deposition.

 

Clastic sedimentary rocks are made of pieces of rock or mineral grains that have been broken from preexisting rock. These particles and grains have become solid rock by the processes of compaction or cementation of sediments. Some clastic rocks are conglomerate, shale, breccia, gray and red sandstone, siltstone, and graywacke.

 

 

Non-clastic sedimentary rocks form from the precipitation (Precipitation is the separating of a solid from a solution) of minerals from ocean water or from the breakdown of the shells and bones of sea creatures. Sea animals such as coral produce calcium carbonate solutions that harden to form rock. As the chemicals, that comes from the mineral or biological precipitation, mix with sediments on the floor of the ocean or lake they crystallize and grow in the spaces around the sediment. When these crystals grow large enough to fill the spaces they harden and form a solid rock.

Some non-clastic rocks are limestone, chert, dolostone, gypsum, halite (rock salt), diatomite, and chalk.

 

Organic sedimentary rocks form from the build up and decay of plant and animal material. This usually forms in swamp regions in which there is an abundant supply of growing vegetation and low amounts of oxygen. The vegetation builds so quickly that new layers of vegetation bury the dead and decaying material very quickly. The bacteria that decay the vegetation need oxygen to survive. Because these decaying layers are buried so fast the bacteria use up what oxygen there is available and can not finish the decomposition of the vegetation. The overlaying layers become so heavy that they squeeze out the water and other compounds that aid in decay.

This compressed vegetation forms coal. The longer and deeper that coal is buried makes it of higher quality. Peat is the first stage of coal formation. Lignite is the next grade of coal followed by bituminous and the highest grade, anthracite. Anthracite is actually a metamorphic rock. It forms during mountain building when compaction and friction are extremely high. This form of coal burns very hot and almost smokeless. It is used in the production of high grade steel.

 

Shale is one of the most common sedimentary rocks. It is composed of silt or clay that has been compacted or squeezed together to form a solid rock. Shale is usually found in thin layers. The silt or clay that composes shale is made of very small pieces of weathered rock. The pieces are from 1/16 to 1/256 of a millimeter in diameter. The color of a sample of shale is that of the clay or silt that it was formed from.

 

 

Sandstone is a clastic sedimentary rock that forms from the cementing together of sand sized grains forming a solid rock. Quartz is the most abundant mineral that forms sandstone. Calcium carbonate, silica, or iron has been added to the water that is in contact with the sand grains. These minerals grow crystals in the spaces around the sand grains. As the crystals fill the gaps the individual sand grains are now transformed into a solid rock.

 

 

Limestone is the most abundant of the non-clastic sedimentary rocks. Limestone is produced from the mineral calcite (calcium carbonate) and sediment. The main source of limestone is the limy ooze formed in the ocean. The calcium carbonate can be precipitated from ocean water or it can be formed from sea creatures that secrete lime such as algae and coral.

Chalk is another type of limestone that is made up of very small single-celled organisms. Chalk is usually white or gray in color.

Limestone can easily be dissolved by acids. If you drop vinegar on limestone it will fizz. Put a limestone rock into a plastic jar and cover it with vinegar. Cover the jar and watch the bubbling of the calcium carbonate and also the disintegration of the rock over a few days.

 

Limestone caves are an interesting geological feature. They form because the limestone deposits located under the ground are chemically dissolved by moving ground water. The ground water contains minerals that make the water slightly acidic. When an acid comes into contact with a rock that is composed of calcium carbonate a chemical reaction takes place. The acid "eats" the limestone. The calcium carbonate then goes into the ground water which moves down farther into the cave. The water will find its way into small crack and crevasses. The dripping water will create formations called stalactites and stalagmites.

Stalactites (they grow from the ceiling)and stalagmites (they grow from the floor) are not technically limestone. They form in caves because as the limestone is dissolved calcium carbonate is put into solution in the ground water. This solution drips through crack and slowly forms stalactites and stalagmites.

The photo to your right shows both stalactites and stalagmites growing together in Jewel Cave National Park in South Dakota.

 

Conglomerate is a clastic sedimentary rock that forms the cementing of rounded cobble and pebble sized rock fragments. Conglomerate is formed by river movement or ocean wave action. The cementing agents that fill the spaces to form the solid rock conglomerate are silica, calcite, or iron oxides.

Notice in the photo above the rounded rock particles in the conglomerate. These rounded particles make conglomerate different from the next rock you are about to study, breccia.

 

Breccia is formed in a very similar fashion to conglomerate. The difference between the two rocks is that breccia's rock fragments are very sharp and angular. These rock fragments have not been transported by water, wind, or glaciers long enough to be rounded and smoothed like in the conglomerate. The cementing agents silica, calcite (CaCO3), and iron oxides are the same as in conglomerate.

 

 

Write the answers to the following questions in complete sentences on a piece of paper.

 

1.

In your own words describe the process of weathering.

2.

What is deposition?

3.

What are the three ways that a sedimentary rock forms?

4.

How does a limestone cave form?

 

Metamorphic Rocks Lesson #14

Welcome to the lesson "Metamorphic Rocks".

 

Rocks are formed on Earth as igneous, sedimentary, or metamorphic rocks. Igneous rocks form when rocks are heated to the melting point which forms magma. Sedimentary rocks are formed from the cementing together of sediments, or from the compaction (squeezing together) of sediments, or from the recrystallization of new mineral grains which are larger than the original crystals. Metamorphic rocks form from heat and pressure changing the original or parent rock into a completely new rock. The parent rock can be either sedimentary, igneous, or even another metamorphic rock. The word "metamorphic" comes from Greek and means "To Change Form".

The diagram above shows you how the rocks on Earth have been changed continually over time from one rock type to another. This changing of rock types is called the "Rock Cycle".

 

Solid rock can be changed into a new rock by stresses that cause an increase in heat and pressure. There are 3 main agents that cause metamorphism. Factors that cause an increase in Temperature, Pressure, and Chemical changes are the three agents that we are going to study.

Temperature increases can be caused by layers of sediments being buried deeper and deeper under the surface of the Earth. As we descend into the earth the temperature increases about 25 degrees Celsius for every kilometer that we descend. The deeper the layers are buried the hotter the temperatures become. The great weight of these layers also causes an increase in pressure, which in turn, causes an increase in temperature.

The descending of rock layers at subduction zones causes metamorphism in two ways; the shearing effect of the plates sliding past each other causes the rocks coming in contact with the descending rocks to change. Some of the descending rock will melt because of this friction. When rock melts it is then considered igneous not metamorphic, but the rock next to the melted rock can be changed by the heat and become a metamorphic rock. The diagram above shows you where metamorphic rock (YELLOW ZONE) can be produced at a subduction zone.

There are 3 factors that cause an increase in pressure which also causes the formation of metamorphic rocks. These factors are;

1.

The huge weight of overlying layers of sediments.

2.

Stresses caused by plates colliding in the process of mountain building.

3.

Stresses caused by plates sliding past each other, such as the shearing stresses at the San Andreas fault zone in California.

Factors that cause chemical changes in rocks also contribute to the formation of metamorphic rocks. Very hot fluids and vapors can, because of extreme pressures, fill the pores of existing rocks. These fluids and vapors can cause chemical reactions to take place, that over time, can change the chemical makeup of the parent rock.

Metamorphism can be instantaneous as in the shearing of rocks at plate boundaries or can take millions of years as in the slow cooling of magma buried deep under the surface of the Earth.

 

There are three ways that metamorphic rocks can form. The three types of metamorphism are Contact, Regional, and Dynamic metamorphism.

Contact Metamorphism occurs when magma comes in contact with an already existing body of rock. When this happens the existing rocks temperature rises and also becomes infiltrated with fluid from the magma. The area affected by the contact of magma is usually small, from 1 to 10 kilometers. Contact metamorphism produces non-foliated (rocks without any cleavage) rocks such as marble, quartzite, and hornfels.

In the diagram above magma has pushed its way into layers of limestone, quartz sandstone and shale. The heat generated by the magma chamber has changed these sedimentary rocks into the metamorphic rocks marble, quartzite, an hornfels.

Regional Metamorphism occurs over a much larger area. This metamorphism produces rocks such as gneiss and schist. Regional metamorphism is caused by large geologic processes such as mountain-building. These rocks when exposed to the surface show the unbelievable pressure that cause the rocks to be bent and broken by the mountain building process. Regional metamorphism usually produces foliated rocks such as gneiss and schist.

Dynamic Metamorphism also occurs because of mountain-building. These huge forces of heat and pressure cause the rocks to be bent, folded, crushed, flattened, and sheared.

 

 

Metamorphic rocks are almost always harder than sedimentary rocks. They are generally as hard and sometimes harder than igneous rocks. They form the roots of many mountain chains and are exposed to the surface after the softer outer layers of rocks are eroded away. Many metamorphic rocks are found in mountainous regions today and are a good indicator that ancient mountains were present in areas that are now low hill or even flat plains. Metamorphic rocks are divided into two categories- Foliates and Non-foliates.

Foliates are composed of large amounts of micas and chlorites. These minerals have very distinct cleavage. Foliated metamorphic rocks will split along cleavage lines that are parallel to the minerals that make up the rock. Slate, as an example, will split into thin sheets. Foliate comes from the Latin word that means sheets, as in the sheets of paper in a book.

 

Silt and clay can become deposited and compressed into the sedimentary rock shale. The layers of shale can become buried deeper and deeper by the process of deposition. Deposition is the laying down of rock forming material by any natural agent (wind, water, glaciers) over time. Because these layers are buried, temperatures and pressures become greater and greater until the shale is changed into slate. Slate is a fine-grained metamorphic rock with perfect cleavage that allows it to split into thin sheets. Slate usually has a light to dark brown streak. Slate is produced by low grade metamorphism, which is caused by relatively low temperatures and pressures.

Slate has been used by man in a variety of ways over the years. One use for slate was in the making of headstones or grave markers. Slate is not very hard and can be carved easily. The problem with slate though is its perfect cleavage. The slate headstones would crack and split along these cleavage planes as water would seep into the cracks and freeze which would lead to expansion. This freeze-thaw, freeze-thaw over time would split the headstone. Today headstones are made of a variety of rocks, with granite and marble being two of the most widely used rocks. Slate was also used for chalk boards. The black color was good as a background and the rock cleaned easily with water. Today it is not very advantageous to use this rock because of its weight and the splitting and cracking over time.

 

Schist is a medium grade metamorphic rock. This means that it has been subjected to more heat and pressure than slate, which is a low grade metamorphic rock. As you can see in the photo above schist is a more coarse grained rock. The individual grains of minerals can be seen by the naked eye. Many of the original minerals have been altered into flakes. Because it has been squeezed harder than slate it is often found folded and crumpled. Schists are usually named by the main minerals that they are formed from. Bitotite mica schist, hornblende schist, garnet mica schist, and talc schist are some examples of this.

 

 

Gneiss is a high grade metamorphic rock. This means that gneiss has been subjected to more heat and pressure than schist. Gneiss is coarser than schist and has distinct banding. This banding has alternating layers that are composed of different minerals. The minerals that compose gneiss are the same as granite. Feldspar is the most important mineral that makes up gneiss along with mica and quartz. Gneiss can be formed from a sedimentary rock such as sandstone or shale, or it can be formed from the metamorphism of the igneouse rock grantite. Gneiss can be used by man as paving and building stone.

 

 

Non-Foliates are metamorphic rocks that have no cleavage at all. Quartzite and marble are two examples of non-foliates that we are going to study.

 

Quartzite is composed of sandstone that has been metamorphosed. Quartzite is much harder than the parent rock sandstone. It forms from sandstone that has come into contact with deeply buried magmas. Quartzite looks similar to its parent rock. The best way to tell quartzite from sandstone is to break the rocks. Sandstone will shatter into many individual grains of sand while quartzite will break across the grains.

 

 

Marble is metamorphosed limestone or dolomite. Both limestone and dolomite have a large concentration of calcium carbonate (CaCO3). Marble has many different sizes of crystals. Marble has many color variances due to the impurities present at formation. Some of the different colors of marble are white, red, black, mottled and banded, gray, pink, and green.

Marble is much harder than its parent rock. This allows it to take a polish which makes it a good material for use as a building material, making sink tops, bathtubs, and a carving stone for artists. Today, headstones are made from marble and granite because both of these rocks weather very slowly and carve well with sharp edges.

Marble is quarried in Vermont, Tennessee, Missouri, Georgia, and Alabama.

 

Write the answers to the following questions in complete sentences on a piece of paper.

1.   

Write a definition in your own words of what a metamorphic rock is.

2.   

What are the three agents of metamorphism?

3.   

What are the three types of metamorphism?

4.   

In your own words write a definition of the rock cycle.

Rocks and Minerals Slide Show

Mineral Show 1

Mineral information is presented here; Pictures of minerals are found at the bottom of the page.

 

Augite is a greenish-black mineral that is found in many igneous rocks. It is found in many basic and ultra-basic igneous rocks such as gabbro and basalt. Augite has a hardness of 5-6.5 with a vitreous luster and a prismatic cleavage.

 Mineral information is presented here; Pictures of minerals are found at the bottom of the page

 

Magnetite is a mineral that has a very high iron content. Magnetite has a black or brownish-red color and a black streak. It has a hardness of about 6 on the Mohs hardness scale. It is one of two minerals in the world that is naturally magnetic. Magnetite, also known as lodestone, is found throughout the United States. Magnetite is an important source of iron ore and occurs in many igneous rocks.

 

Milky quartz is a common mineral that is found in many different types of rocks. The chemical formula is silicon oxide (SiO2). One type of quartz is easily identified by its hexagonal crystals, but quartz can also be found in a large mass. Quartz can be broken or weathered into the tiny pieces we know as sand. Quartz is a very hard mineral and in fact is the hardest of the common minerals. Quartz is number seven on the Mohs hardness scale. Quartz is also chemically stable, which means that it weathers very slowly.

Quartz can be colored yellow, milky white, rose, smoky (brown or black), and the best known of the colored crystals amethyst, which is purple. Impurities in the rock at the time of formation causes the quartz crystal to have these different colors.

Quartz is used by humans in producing optical instruments and electical devices. It is also used to make sandpaper and grinding tools.

 

Galena is an important source of lead. Galena's chemical symbol is PbS, which is lead and sulfur. Galena may also contain silver. The United States is the leading producer of lead in the world. Lead was used in pencils and paint until it was found to be poisonous to humans . Today pencil "lead" is made of another mineral called graphite. Lead is used for fishing weights.

Galena is an lead sulfide and the main source of lead. Galena usually occurs in cubic crystals. If you hit a specimen of galena with a hammer it will shatter into small perfect cubic crystals. It has a metallic luster and a black to dark gray color and streak. Galena has a hardness of about 2.5 on Mohs hardness scale which is about as hard as your finger nail.

Galena is mined in Missouri, Idaho, Utah, Oklahoma, Colorado, British Columbia of Canada, and Mexico.

 

Pyrite is also known as iron sulfide. It is one of the most common minerals on the Earth's surface. Many people call pyrite "Fools Gold" because the crystal resemble gold in color. Pyrite is much harder than gold and it looses its glitter quickly when exposed to the air. In fact when it is rubbed on a streak plate the streak will be green to dark gray. Pyrite has a hardness of 6.5 on the Mohs hardness scale. Its cleavage is cubic or not distinct.

 

 

Mica is a mineral that can be split into very thin sheets. These sheets can be so thin that 1000 can be layered into mica 1 inch high. Mica can be clear, black, green, red, yellow, and brown. Clear mica is called Muscovite because it is found near Moscow, Russia and was used as window glass in the Muscovite's homes. Muscovite contains water which helps to make it clear. Biotite mica is dark green to black in color because it contains iron and magnesium.

Mica is mined in Brazil, India, many parts of Africa, Canada, and the United States. It is used in the manufacturing of electronic and electrical devices.

 

Hornblende is a mineral that contains magnesium, iron, silica and aluminum. Hornblende is black, brown and green in color. It occurs in crystals of many igneous rocks.

 

 

Feldspar is the most abundant mineral in rocks that are located at or near the earth's surface. Feldspar can have glassy white, blue, green, or red crystals. All feldspars contain silica and aluminum.

When feldspars are exposed to the atmosphere they break down or weather easily. When they are broken down, feldspar forms other minerals, many of which are clay minerals. Feldspars also contain potassium which is a major nutrient for plant growth.

The clays formed by weathered feldspar are used by pottery manufacturing plants. Kaolinite is the highest quality of the feldspar clays used by potters.

Feldspar is number 6 on the Mohs hardness scale.

Orthoclase has a chemical make up of KAlSi3O8. Orthoclase is usually pink but can be white, grey, green, and pink.

Plagioclase is a form of feldspar that has a chemical make up of NaAlSi3O8. Plagioclase is usually white but can also be grey and greenish white. This mineral was abundant in the Moon rock samples.

 

Pyroxene is one of the three main minerals that makes up basalt. The most common pyroxenes are magnesium, calcium, and iron silicates. A common pyroxene is augite which is very abundant in many igneous rocks such as basalt and gabbro.

 

 

Calcite is pure calcium carbonate (CaCO3). It is found in limestone and marble. It is the cementing agent that binds sediments together into sedimentary rocks. Marble is metamorphosed (changed by heat and pressure) limestone. The crystals formed from pure calcite are in the form of a perfect rhomboid. A rhomboid is a six-sided solid object in which the opposite sides are parallel. It has perfect cleavage in three directions. If you hit calcite with a hammer it will break into smaller but perfectly shaped rhomboids. Calcite is number two on Mohs hardness scale. Calcite is the material that forms stalactites and stalagmites in caves.

Calcite is used as a fertilizer, cement, chalk, building stone, and for the manufacture of optical instruments.

 

Mineral Show 2

 Mineral information is presented here; Pictures of minerals are found at the bottom of the page.

 

Talc is a mineral that has perfect cleavage and a greasy or soapy feel. It is given the distinction of being number 1 on Mohs hardness scale. Talc is also called soapstone which is used by artists for sculptures. Talc can be ground up into talcum powder. Ground talc is also used to make crayons, paint, paper, and soap. Talc is quarried in many Northeastern states of the United States.

 

Dolomite is both a mineral and a rock. Dolomite is a calcium-magnesium carbonate. It is very similar to calcite and limestone in its chemical make up. Dolomite is white or light pink in color. It has a hardness of 3.5 - 4 and only will react to acid when it is heated or in powdered form. Dolomite is used as a building stone and as a source of magnesium.

 

Graphite and diamond are both pure carbon. The difference is the amount of heat and pressure that has been put onto the two minerals. Diamond is the hardest natural element on Earth with a hardness of 10 which is the maximum on the Mohs hardness scale. Graphite is a very soft mineral with a hardness between 1 and 2. Graphite has a black streak and was probably formed by the metamorphism of plant remains or by the crystallization of ancient magmas.

Today graphite is used for "lead" in pencils. Lead is poisonous to humans and has not been used for many years in pencils. Graphite is also used in the paint industry.

 

Hematite is the most important source of iron ore in the world. The production of iron has been important to nations of the world for over 2500 years. Today the addition of other minerals to iron has lead to the production of steel which is vital to the economy of the major countries on Earth. Hematite has a red or black color but the streak is always red. The iron in the hematite turns red when it comes in contact with water and oxygen. In other words this rock is rusted!!

Hematite has a metallic or earthy luster. The hardness of hematite is about 5 on Mohs hardness scale. It has no cleavage and breaks with an uneven fracture. The reddish landscape of Mars is due to the oxidized iron on its surface. This tells us that water and oxygen must have been present on Mars at one time.

Hematite is mined in the Lake Superior and Appalachian mountain regions of the United States. Small deposits are found in many states of the union. Canada and Russia are leading countries in the mining of iron ore.

 

Kaolinite is a clay mineral which is formed by the weathering of feldspar. It is one of the most common minerals on Earth. Kaolinite can be found in all parts of the Earth. It is very soft with a hardness of 2-2.5. It has a color of white, pink or grey and a streak of white. The chemical make up is Al2 Si2 O5 (OH)4.

Kaolinite is used in the ceramics industry for the production of clay products.

 

Pyrite is also known as iron sulfide. It is one of the most common minerals on the Earth's surface. Many people call pyrite "Fools Gold" because the crystal resemble gold in color. Pyrite is much harder than gold and it looses its glitter quickly when exposed to the air. In fact when it is rubbed on a streak plate the streak will be green to dark gray. Pyrite has a hardness of 6.5 on the Mohs hardness scale. Its cleavage is cubic or not distinct.

 

Quartz is a common mineral that is found in many different types of rocks. The chemical formula is Silicon oxide (SiO2). One type of quartz is easily identified by its hexagonal crystals, but quartz can also be found in a large mass. Quartz can be broken or weathered into the tiny pieces we know as sand. Quartz is a very hard mineral and in fact is the hardest of the common minerals. Quartz is number seven on the Mohs hardness scale. Quartz is also chemically stable, which means that it weathers very slowly.

Quartz can be colored yellow, milky white, rose, smoky (brown or black), and the best known of the colored crystals amethyst, which is purple. Impurities in the rock at the time of formation causes the quartz crystal to have these different colors.

Quartz is used by humans in producing optical instruments and electical devices. It is also used to make sandpaper and grinding tools.

 

 

 

 

Igneous Rocks

Mineral information is presented here; Pictures of minerals are found at the bottom of the page.

 

Basalts are dark colored, fine-grained extrusive rock. The mineral grains are so fine that they are impossible to distinguish with the naked eye or even a magnifying glass. They are the most widespread of all the igneous rocks. Most basalts are volcanic in origin and were formed by the rapid cooling and hardening of the lava flows. Some basalts are intrusive having cooled inside the Earth's interior.

 

Granite is an igneous rock that is composed of four minerals. These minerals are quartz, feldspar, mica, and usually hornblende. Granite forms as magma cools far under the earth's surface. Because it hardens deep underground it cools very slowly. This allows crystals of the four minerals to grow large enough to be easily seen by the naked eye. Look at the photo of granite above, notice the different crystals in the rock.

Granite is an excellent material for building bridges and buildings because it can withstand thousands of pounds of pressure. It is also used for monuments because it weathers slowly. Engravings in the granite can be read for hundreds of years, making the rock more valuable.

Granite is quarried in many places in the world including the United States. The State of New Hampshire has the nickname "Granite State" because of the amount of granite in the mountains of that beautiful state. The Canadian Shield of North America contains huge outcroppings (surface rocks) of granite.

 

Dacite is an extrusive igneous rock. The principle minerals that make up dacite are plagioclase, quartz, pyroxene, or hornblende.

 

 

Obsidian is a very shiny natural volcanic glass. When obsidian breaks it fractures with a distinct conchoidal fracture. Notice in the photo to the left how it fractures. Obsidian is produced when lava cools very quickly. The lava coo ls so quickly that no crystals can form.

When people make glass they melt silica rocks like sand and quartz then cool it rapidly by placing it in water. Obsidian is produced in nature in a similar way.

Obsidian is usually black or a very dark green, but it can also be found in an almost clear form.

Ancient people throughout the world have used obsidian for arrowheads, knives, spearheads, and cutting tools of all kinds. Today obsidian is used as a scalpel by doctors in very sensitive eye operations.

 

Gabbro is a dark-colored, coarse-grained intrusive igneous rock. Gabbro is very similar to basalt in its mineral make up. It is composed mostly of the mineral plagioclase feldspar with smaller amounts of pyroxene and olivine.

 

Rhyolite is very closely related to granite. The difference is rhyolite has much finer crystals. These crystals are so small that they can not be seen by the naked eye. Rhyolite is an extrusive igneous rock having cooled much more rapidly than granite, giving it a glassy appearance. The minerals that make up rhyolite are quartz, feldspar, mica, and hornblende.

 

 

Pumice is a very light colored, frothy volcanic rock. Pumice is formed from lava that is full of gas. The lava is ejected and shot through the air during an eruption. As the lava hurtles through the air it cools and the gases escape leaving the rock full of holes.

Pumice is so light that it actually floats on water. Huge pumice blocks have been seen floating on the ocean after large eruptions. Some lava blocks are large enough to carry small animals.

Pumice is ground up and used today in soaps, abrasive cleansers, and also in polishes.

 

Sedimentary Rocks

Mineral information is presented here; Pictures of minerals are found at the bottom of the page.

 

Conglomerate is a clastic sedimentary rock that forms from the cementing of rounded cobble and pebble sized rock fragments. Conglomerate is formed by river movement or ocean wave action. The cementing agents that fill the spaces to form the solid rock conglomerate are silica, calcite, or iron oxides.

Notice in the photo above the rounded rock particles in the conglomerate. These rounded particles make conglomerate different from breccia.

 

Breccia is formed in a very similar fashion to conglomerate. The difference between the two rocks is that breccia's rock fragments are very sharp and angular. These rock fragments have not been transported by water, wind, or glaciers long enough to be rounded and smoothed like in the conglomerate. The cementing agents silica, calcite (CaCO3), and iron oxides are the same as in conglomerate.

 

 

Chert is a very hard sedimentary rock that is usually found in nodules in limestone. Chert is light gray to dark gray in color. It probably formed from the remains of ancient sea sponges or other ocean animals that have been fossilized. Silica has replaced the tissue forming the sedimentary rock. Flint is a very dark form of chert. It breaks like obsidian with conchoidal fractures making it widely used by ancient people to make arrowheads, spear heads, and knives.

 

 

Halite is common table salt. It forms where brakish (salty) lakes or sea beds dry up. This evaporation of the water causes the salt to precipitate forming the salt crystals. Halite frequently occurs in crystal form. It is usually colorless but can be reddish brown because of iron oxides in the water that it forms in. Halite has perfect cleavage and a hardness of 2.5 on the Mohs hardness scale.

 

 

Limestone is the most abundant of the non-clastic sedimentary rocks. Limestone is produced from the mineral calcite (calcium carbonate) and sediment. The main source of limestone is the limy ooze formed in the ocean. The calcium carbonate can be precipitated from ocean water or it can be formed from sea creatures that secrete lime such as algae and coral.

Chalk is another type of limestone that is made up of very small single-celled organisms. Chalk is usually white or gray in color.

Limestone can easily be dissolved by acids. If you drop vinegar on limestone it will fizz. Put a limestone rock into a plastic jar and cover it with vinegar. Cover the jar and watch the bubbling of the calcium carbonate and also the disintegration of the rock over a few days.

 

Sandstone is a clastic sedimentary rock that forms from the cementing together of sand sized grains forming a solid rock. Quartz is the most abundant mineral that forms sandstone. Calcium carbonate, silica, or iron has been added to the water that is in contact with the sand grains. These minerals grow crystals in the spaces around the sand grains. As the crystals fill the gaps the individual sand grains are now transformed into a solid rock.

 

 

Metamorphic Rocks

Mineral information is presented here; Pictures of minerals are found at the bottom of the page.

 

Marble is metamorphosed limestone or dolomite. Both limestone and dolomite have a large concentration of calcium carbonate (CaCO3). Marble has many different sizes of crystals. Marble has many color variances due to the impurities present at formation. Some of the different colors of marble are white, red, black, mottled and banded, gray, pink, and green.

Marble is much harder than its parent rock. This allows it to take a polish which makes it a good material for use as a building material, making sink tops, bathtubs, and a carving stone for artists. Today, headstones are made from marble and granite because both of these rocks weather very slowly and carve well with sharp edges.

Marble is quarried in Vermont, Tennessee, Missouri, Georgia, and Alabama.

 

Slate is a fine-grained metamorphic rock with perfect cleavage that allows it to split into thin sheets. Slate usually has a light to dark brown streak. Slate is produced by low grade metamorphism, which is caused by relatively low temperatures and pressures.

Slate has been used by man in a variety of ways over the years. One use for slate was in the making of headstones or grave markers. Slate is not very hard and can be engraved easily. The problem with slate though is its perfect cleavage. The slate headstones would crack and split along these cleavage planes. This is not a desirable attribute for a head stone. Slate was also used for chalk boards. The black color was good as a background and the rock cleaned easily with water. Today it is not very advantageous to use this rock because of its weight and the splitting and cracking over time.

 

Schist is a medium grade metamorphic rock. This means that it has been subjected to more heat and pressure than slate, which is a low grade metamorphic rock. As you can see in the photo above schist is a more coarse grained rock. The individual grains of minerals can be seen by the naked eye. Many of the original minerals have been altered into flakes. Because it has been squeezed harder than slate it is often found folded and crumpled. Schists are usually named by the main mineral from which they are formed. Bitotite mica schist, hornblende schist, garnet mica schist, and talc schist are some examples of this.

 

Gneiss is a high grade metamorphic rock. This means that gneiss has been subjected to more heat and pressure than schist. Gneiss is coarser than schist and has distinct banding. This banding has alternating layers that are composed of different minerals. The minerals that compose gneiss are the same as granite. Feldspar is the most important mineral that makes up gneiss along with mica and quartz. Gneiss can be formed from a sedimentary rock such as sandstone or shale, or it can be formed from the metamorphism of the igneouse rock grantite. Gneiss can be used by man as paving and building stone.

 

 

Quartzite is composed of sandstone that has been metamorphosed. Quartzite is much harder than the parent rock, sandstone. It forms from sandstone that has come into contact with deeply buried magmas. Quartzite looks similar to its parent rock. The best way to tell quartzite from sandstone is to break the rocks. Sandstone will shatter into many individual grains of sand while quartzite will break across the grains.

 

 

Organic sedimentary rocks form from the build up and decay of plant and animal material. This usually forms in swamp regions in which there is an abundant supply of growing vegetation and low amounts of oxygen. The vegetation builds so quickly that new layers of vegetation bury the dead and decaying material very quickly. The bacteria that decay the vegetation need oxygen to survive. Because these decaying layers are buried so fast the bacteria use up what oxygen there is available and can not finish the decomposition of the vegetation. The overlaying layers become so heavy that they squeeze out the water and other compounds that aid in decay.

This compressed vegetation forms coal. The longer and deeper that coal is buried makes it of higher quality. Peat is the first stage of coal formation. Lignite is the next grade of coal followed by bituminous and the highest grade, anthracite.

Anthracite is actually a metamorphic rock. It forms during mountain building when compaction and friction are extremely high. This form of coal burns very hot and almost smokeless. It is used in the production of high grade steel.

Chapter #4 Copymaster: Test, Reviews, AnswerKeys, Chapter Schedule

Rocks and Minerals Lesson Plan

Rocks and Minerals

 

 

In the chapter "Rocks and Minerals" the students will have the opportunity to work with 30 minerals and rocks in a hands-on data collection center. Then the students will study the concepts and processes associated with those same minerals and rocks at the computer center. You will need to locate the following materials to allow your students to complete the lessons.

Materials:

A "Rocks and Minerals" lab kit which includes the following items;

 

  

Plastic boxes to hold the lab materials and the rock and mineral specimen. The number of boxes will be determined by the number of groups that your class has. I would suggest no more than four students per group.

  

30 rocks and minerals specimen

1.   

Lesson 1-granite, biotite mica , white feldspar, hornblende, milky 
quartz 


2.   

Lesson 2-talc, galena, hematite, magnetite, calcite


3.   

Lesson 3-pumice, obsidian, basalt, gabbro, rhyolite

4.   

Lesson 4-conglomerate, limestone, shale, breccia, and gray sandstone

5.   

Lesson 5-slate, marble, schist, gneiss, quartzite
Lesson 6-anthracite coal, red sandstone, kaolinite, rose quartz, halite



  

Lab materials

glass slides, pennies, iron nails, eye droppers and bottles, vinegar, streak plates, magnets, and magnifying lenses.

You will need one each of the above testing materials for each group.

  

Data collection sheets

Each student should receive data collection sheets which will cover all 30 rocks and minerals specimen. The students will perform 11 tests and collect the data from the different tests on each rock or mineral sample.


Color- The students will look at the sample and write down the color that they see in the sample.


Streak -The students will scratch the specimen across the streak plate to determine the color of the streak.


Luster- The students will determine if the mineral has a metallic or non-metallic luster. If the luster is non-metallic the student will determine if the sample is earthy, pearly, vitreous, or greasy.


Acid Test- The students will use an eyedropper to put a drop of vinegar onto the sample and watch with the hand lens to see if any "FIZZING" occurs. If a chemical reaction occurs with the dilute acid then the students are able to determine if any calcium carbonate is present.


Magnetism- The students will touch the specimen with a magnet to determine if the specimen is magnetic.


Hardness Tests- The tests are used to determine the relative hardness of a rock or mineral. To determine the hardness the students will scratch the testing material (ie: glass slide, penny etc.) with the rock sample to determine which is harder. 
When the students are testing the hardness they can stop when their sample is found to be softer than the testing material.

Fingernail- The students will scratch the rock specimen with their thumbnail to determine if the sample is harder or softer than their nail. If the mineral scratches their nail then the sample is harder than the nail. The students can X the column under the fingernail and proceed to the next test. Hardness = 2.5 on Mohs hardness scale.


Penny- The students will scratch a copper penny to determine if the specimen is harder or softer than the penny. Hardness = 3 on Mohs hardness scale.


Iron Nail- The students will continue to test the samples hardness with the iron nail. Hardness = 4.5 on Mohs hardness scale.


Glass Slide- The glass slide is the last hardness test. If the sample is harder than the glass slide explain to the students that the sample is above 6 on the hardness scale and there are not many common minerals that are that hard. Quartz is the hardest of the common minerals at 7 on the hardness scale.


Layers/Bands/Crystals- The students will examine the rock specimen for sedimentary layers, metamorphic bands, and crystal formation. Explain to the students that there is a difference between bands and layers. Have the students record what they see on their data collection chart.


 

The first lesson "Rocks " works with the following specimen of rocks and minerals; Granite, biotite mica, quartz, feldspar, and hornblende. At the computer center the students will study the concepts and processes that form rocks.

 

In the second lesson "Minerals " the students will work with the following minerals; Galena, magnetite, hematite, talc, and calcite. The students will be exposed to the processes and concepts associated with the formation of minerals.

 

The third lesson deals with igneous rocks. The students will become aware of the processes that cause the formation of igneous rocks. The students will work hands-on with the following rocks; pumice, obsidian, gabbro, basalt, and rhyolite.

 

The fourth lesson involves the students learning about the processes that form sedimentary rocks . They will work hands-on with the following rocks; conglomerate, breccia, limestone, gray sandstone, and shale.

 

The fifth lesson in this series involves teaching about the concepts and processes involved in the formation of metamorphic rocks . The students will work hands-on with the following rock samples; slate, schist, gneiss, white marble, quartzite.

 

The sixth lesson in this series involves teaching about the processes of coal and fossil formation. The students will be working hands-on with the following samples of rocks and minerals; Anthracite coal , halite, pyrite, kaolinite, dolomite, and graphite.

 

 

Rocks and Minerals Lesson Chart

Chapter 4 - Chart

Chapter 4 Student Vocabulary

Rocks and Minerals

Lesson 10 Rocks

Name_________________

1. The age of the Earth-

 

 

 

 

2. How the layers cooled-

 

 

 

3. Rocks-

 

(a)

(b)

(c)

 

4. Minerals-

 

 

 

 

5. Soil-

 

 

 

6. Rock Cycle-

 

Chapter 4 - Student Rock Vocab 

Chapter 4 Teacher Vocabulary

Rocks and Minerals

Lesson 10 Rocks

Name_________________

1. The age of the Earth-

The Earth is about 4.6 billion years old.

 

 

2. How the layers cooled-

As the Earth cooled the heaviest and densest materials sank to the center, and the lightest materials rose to the top. The heaviest materials are the metals iron and nickel, which makes up the inner and outer cores. The lightest materials are rock and make up the crust and upper most region of the mantle.

 

3. Rocks-

Rocks are composed of two or more minerals. These minerals have been 1) cemented together 2) squeezed and heated together, or 3) melted and cooled together Rocks make up the vast majority of the Earth's crust. The two most common rocks on the crust are granite and basalts.

4. Minerals-

A mineral is a solid that is composed of one substance that occurs naturally on Earth.

 

5. Soil-

Soil is composed of very small, weathered fragments of rock along with organic (decomposed or decomposing plant and animal material) material.

 

6. Rock Cycle-

The rock cycle is the process in which igneous, sedimentary, and metamorphic rocks are changed over time. Igneous rocks are formed by volcanic activity. Metamorphic rocks are igneous, sedimentary, or other metamorphic rocks that have been changed by heat, pressure, chemical means, or a combination of all or some of the above. Sedimentary rocks are formed from the weathering of all of the rock types and the cementing, compressing, or recrystallization of the sediments.

 

Chapter 4 - Test key rock cycle

Chapter 4 Review

SCIENCE REVIEW

CHAPTER 4

Name

_____________________

 

Write a definition for the following terms.

1. Rock-

 

 

2. Mineral-

 

 

3. Weathering-

 

 

4. Igneous rocks-

 

 

5. Sedimentary rocks-

 

 

6. Metamorphic rocks-

 

 

7. Draw a diagram and describe the rock cycle-

 

 

 

 

8. Name the most common rock found on the surface of the

Earth.

 

9-12. Name the four minerals that make up granite.

 

13. Describe what the term, property of a mineral means.

 

14-21. Match the following igneous terms with its corresponding definition.

14. _____Sill a. An intrusive igneous body that runs through an existing layer of rock.

15. _____Dike b. A very large intrusive igneous body that is larger than 100 square miles.

16. _____Batholith c. A type of igneous rock that is

formed under the surface of the Earth.

17. _____Laccolith d. Molten rock under the surface of the Earth.

18. _____Intrusive e. Molten rock on the surface of the Earth.

19. _____Extrusive f. A type of igneous rock that is formed on the surface of the Earth.

20. _____Magma g. A small intrusive igneous body.

21. ______Lava h. An intrusive igneous body that runs parallel with existing rock layers.

 

22- Match the following terms with its corresponding definition.

 

22. _____Metallic a. A test to determine the true color of a mineral.

23. _____Non-metallic b. A property that describes how a mineral breaks into flat planes.

24. _____Streak c. A mineral that conducts electricity.

25. _____Hardness d. A property of a mineral that is measured by the Mohs scale.

26. _____Cleavage e. A property of a mineral that measures how it reflects light.

27. _____Luster f. A mineral that does not conduct electricity.

 

28-42 Write the correct term

rock or mineral after each word below.

 

Pumice___________

Talc______________

Gabbro___________

Granite____________

Magnetite__________

Hornblende_________

Hematite___________

Mica______________

Obsidian___________

Quartz____________

Galena____________

Feldspar___________

Basalt_____________

Calcite_____________

Rhyolite___________

Chapter 4 Test

SCIENCE TEST

CHAPTER 4

Name

_____________________

 

1. What is the name of the most common rock on the surface of the Earth?

 

 

2. In your own words give a definition of the term, ROCK.

 

 

 

3. What are the four minerals that are usually found in granite?

 

 

 

4. What is weathering?

 

 

 

5. What are the three types of rocks?

 

 

 

6. Draw a diagram and explain what happens in the rock cycle.

 

Chapter 4 Review Answer Key

SCIENCE REVIEW

CHAPTER 4

Name

_____________________

 

Write a definition for the following terms.

1. Rock-

Rocks are made of two or more different minerals that have been 1) cemented together, or 2) squeezed and heated together, or 3) melted and cooled together. Rocks make up the majority of the Earth's crust. One of the most common rock is granite.

 

2. Mineral- A mineral is a solid material, made of one substance, that occurs naturally on Earth.

Most of the common minerals are made of crystals. A Crystal is a solid formed by a repeating, three-dimensional pattern of atoms, ions, or molecules and having fixed distances between the different parts.

 

3. Weathering-

The break down of rock by wind, water, or ice into smaller pieces.

 

4. Igneous rocks-Igneous rocks start as magma. The magma (molten rock under the surface) and lava (molten rock on the surface) hardens into igneous rock.

 

5. Sedimentary rocks- Sedimentary rocks are formed from the breaking apart of other rocks (igneous, metamorphic, or sedimentary rocks) and the cementation, compaction and recrystallization of these broken pieces of rock.

 

6. Metamorphic rocks- Metamorphic rocks form from heat and pressure changing the original or parent rock into a completely new rock. The parent rock can be either sedimentary, igneous, or even another metamorphic rock.

 

7. Draw a diagram and describe the rock cycle-

 Chapter 4 - Test Key Rock Cycle

 

8. Name the most common rock found on the surface of the Earth.

One of the most common rock is granite.

9-12. Name the four minerals that make up granite.

The four minerals that make up granite are feldspar, quartz, mica, and hornblende.

13. Describe what a property of a mineral is.

A mineral is a solid material, made of one substance, that occurs naturally on Earth.

 

14-21. Match the following igneous terms with its corresponding definition. 


14. __H__Sill a. An intrusive igneous body that runs through an existing layer of rock.


15. __ A __Dike b. A very large intrusive igneous body that is larger than 100 square miles.


16. __ B __Batholith c. An igneous rock that is formed under the surface of the Earth.


17. __ G __Laccolith d. Molten rock under the surface of the Earth.


18. __ C __Intrusive e. Molten rock on the surface of the Earth.


19. __ F __Extrusive F. An igneous rock that is formed on the surface of the Earth.

20. __ D __Magma g. A small intrusive igneous body.


21. __ E __Lava h. An intrusive igneous body that runs parallel with existing rock layers.



 

22- 28. Match the following terms with its corresponding definition.



22. _ C __Metallic a. A test to determine the true color of a mineral.


23. _ F __Non-metallic b. A property that describes how a mineral breaks into flat planes.


24. __ A __Streak c. A mineral that conducts electricity.

25. __ D __Hardness d. A property of a mineral that is measured by the Mohs scale.

26. __ B __Cleavage e. A property of a mineral that measures how it reflects light.


27. __ E __Luster f. A mineral that does not conduct electricity.







 

28-42 Write the correct term rock or mineral after each word below.



Pumice rock

Talc___ mineral ___


Gabbro___ rock ________

Granite__ Rock ___


Magnetite__ mineral ________


Hornblende_ mineral ___


Hematite___ mineral ________


Mica______ mineral ___

Obsidian___ Rock _____


Quartz____ mineral ___


Galena___ mineral _________


Feldspar___ mineral ______


Basalt____ Rock _____


Calcite____ mineral _____


Rhyolite___ Rock ________

 

Chapter 4 Test Answer Key

SCIENCE TEST

CHAPTER 4

Name

_____Answer Key ___

 

1. What is the name of the most common rock on the surface of the Earth?

Granite

 

 

2. In your own words give a definition of the term, ROCK.

Rocks are made of two or more different minerals that have been 1) cemented together, or 2) squeezed and heated together, or 3) melted and cooled together. Rocks make up the majority of the Earth's crust. One of the most common rock is granite. 

3. What are the four minerals that are found in most granite 

rocks?

Feldspar, mica, quartz, and hornblende

 

4. What is weathering?

The break down of rock by wind, water, or ice into smaller pieces.

 

5. What are the three types of rocks?

Sedimentary, Igneous, and Metamorphic.

 

6. Draw a diagram and explain what happens in the rock 

cycle.

 

Chapter 4 - Test Key

 

 

7. In your own words describe what a mineral is.

A mineral is a solid material, made of one substance, that occurs naturally on Earth.

Most of the common minerals are made of crystals. A Crystal is a solid formed by a repeating, three-dimensional pattern of atoms, ions, or molecules and having fixed distances between the different parts.

 

8. What is the name of the mineral that is magnetic?

Magnetite

 

9. What does the term property of a mineral mean?

A property is a characteristic of a mineral. Properties help scientists to better understand how the mineral was formed and also to help identify a mineral.

 

10-22 Match the following terms with the corresponding letter.

 

10.__ F__ Luster a. A large intrusive igneous body 

larger than 100 square km

11. _A__Batholith b. An intrusive igneous body that 

runs parallel to layers of rock. 

 

12. _D__Non-metallic c. A property of minerals that is 

measured with the Mohs Scale

 

13. _E__Dike d. A mineral that will not 

conduct electricity.

 

14. _G__cleavage e. An intrusive igneous body 

that runs through layers of rock.

 

15. _B__Sill f. A property of minerals that 

indicates the "shininess" of a mineral

16. _C__Hardness g. A property of a mineral that 

describes how a minerals into flat planes.

17. _A__Intrusive a. An igneous rock that is formed under the surface of the Earth.

 

18. _F__Metallic b. An igneous rock that is formed on the surface of the Earth.

 

19. _E__Streak c. Molten rock that has not reached the surface of the Earth.

 

20. _D__Lava d. Molten rock that has reached 

the surface of the Earth. 

 

21. _B__Extrusive e. A test to determine the true 

color of a mineral.

 

22. _C__Magma f. a mineral that conducts electricity

 

23-30 Write the correct term rock or mineral after each word below.

 

Pumice____Rock_______

 

Gabbro____Rock_______

 

Magnetite__Mineral________

 

Hematite___Mineral________

 

Obsidian____Rock_______

 

Galena_____Mineral_______

 

Basalt_____Rock________

 

Rhyolite__Rock__