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Rocks & Minerals: Minerals
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  • 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.
  • Biotite 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Graphite is very similar chemically to a diamond. 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.

  • Rocks & Minerals: Classification Of Rocks

    Classification of Rocks

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