Rocks

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A rock is an aggregate of minerals. It may be made of one mineral or several minerals. Rocks form the crust of the earth and may be hard like granite or soft like clay, gravel, or sandstone.

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The lithosphere is the outer crust of the earth, and down to a depth of 16 km, about 95% of the earth's crust materials are rocks. This shows that rocks are the main material of the earth's outer crus…

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There are about 2,000 minerals on the earth, and only 12 are common rock formers. These common minerals are the main building materials of rocks.

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Silicates are minerals made mainly of silicon and oxygen. About 87% of the minerals in the earth's crust are silicates, so they form the most important mineral group in rock formation.

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Quartz is a silicate mineral composed of silicon and oxygen. It is hard and resistant, so it does not weather easily and often remains in rocks after weaker minerals break down.

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Feldspar is the most abundant silicate mineral, but it is weak and breaks down quickly into clay during chemical weathering. It is also important economically because it is used in ceramics and glass.

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Ferromagnesium is formed when silicon and oxygen combine with iron and magnesium. Rocks containing a lot of these minerals are often weaker because they are easily weathered and eroded.

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Calcite is the most important carbonate mineral. It is usually white but may appear grey, yellow, pink, or brown due to impurities. It reacts vigorously with hydrochloric acid and is a major component…