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.