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Rocks
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Rocks are collections of minerals of similar or different types and there are three main kinds of rocks: igneous, sedimentary and metamorphic rocks.
Igneous Rocks
Volcanic rocks cool rapidly at the surface to form fine crystals. Plutonic rocks are deep-seated and cool slowly to form coarse crystals.
Table: Types of igneous rocks, according to silica and crystalline content (Schroeder, 1984).
Sedimentary Rocks
Sedimentary rocks are formed by the weathering of igneous and metamorphic rocks that are subsequently transported and deposited by water, wind, or ice. Examples of sedimentary rocks are sandstone, shale, limestone, dolomite, rock salt, loess, coal, amber (tree resin), pumice (volcanic lava froth), banded ironstone, rock gypsum, and Dwarka tillite.
Metamorphic Rocks
These are formed when igneous and sedimentary rocks are altered in composition and texture due to pressure and heat. Examples are slate (converted shale), gneiss (converted granite), marble (converted limestone), and quartzite (converted sandstone).
