Petrology is a discipline of geology that studies rocks, minerals and the processes that act on them. Scientists focus on the formation of rocks in this field of science.


Sand, small particles of rock and minerals or other materials, such as coral or slag.

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  • Diabase


    Diabase, an igneous rock similar to basalt in composition, but with coarser grains. See more »

  • Diatomite


    Diatomite, also called Diatomaceous Earth and Kieselguhr, a substance composed primarily of fossilized diatom shells. See more »

  • Fire Clay

    Fire Clay

    Fire Clay, a variety of clay that can withstand intense heat. In general, it is any clay that can withstand temperatures of 2,900 F. See more »

  • Fuller''s Earth

    Fuller''s Earth

    Fuller's Earth, an earthy substance resembling potter's clay, but lacking its putty-like quality. See more »

  • Gneiss


    Gneiss, a coarse-grained metamorphic rock similar in composition to granite. See more »

  • Gravel


    Gravel, small stones found in natural deposits or beds. The stones normally range in size from 14 inch (6 mm) to 2 12 inches (6 cm) in diameter, although the range sometimes is much larger. See more »

  • Limestone


    Limestone, a sedimentary rock that occurs in many areas of the world. Limestone consists chiefly of calcite (calcium carbonate), but it usually contains numerous other minerals, including dolomite, flint, alumina, bitumen, and pyrites. See more »

  • Marl


    Marl, a natural mixture of clay and calcium carbonate. It is a loose, earthy substance, usually gray or bluish in color. See more »

  • Obsidian


    Obsidian, a natural form of glass. It is formed when lava, brought to the surface of the earth by volcanoes, cools so rapidly that crystals have no time to form. See more »

  • Pebble


    Pebble, a smooth, rounded stone usually less than 2 inches (64 mm) in diameter. See more »

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