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Earth-dwellers live on the surface of a huge ball of rock.  Although much of this rock surface is covered by soil and plant life, the landscape is filled with rocks.  Every rock contains mineral substances.  Granite, for instance, contains the minerals feldspar, mica, and quartz, whereas marble is comprised mainly of calcite.  Some rocks are formed from molten material from the Earth's core, while others are formed from animal and plant fossils.  Exposed rocks on the surface of the Earth are constantly subjected to the action of wind, rain, and sometimes waves, which slowly erodes them and wears them away.

The mineral kingdom is a basic group of natural, inorganic objects, and there are more than 5,300 known mineral species.  Silicate minerals containing silicon and oxygen comprise more than 90 percent of the Earth's crust.  Minerals are primarily distinguished by their chemical and physical properties.  Common distinguishing characteristics of minerals include crystal structure, hardness, luster, color, cleavage, and specific gravity.

Certain types of rock, such as granite, sandstone, and limestone, are used for construction or statuary purposes; others such as diamonds and gemstones are often cut, polished, and used in pieces of jewelry; still others, in trace amounts, are used for nutritional purposes.

colorful polished gemstones
Polished Gemstones

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