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.


Slate, a common metamorphic rock that splits into thin, even sheets. Slate consists primarily of such minerals as muscovite (mica), chlorite, and quartz.

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  • How is volcanic ash made?

    How is volcanic ash made?

    Folks in Montana usually expect snow or rain to fall from the sky, not ash. But the 1980 eruption of Mount St. Helens in Washington flung ash across state lines. What is this gritty, gray stuff? See more »

  • Andesite


    Andesite, a fine-grained rock that is widely distributed in the earth's crust. See more »

  • Basalt


    Basalt, one of the most abundant rocks in the earth's crust. It is an igneous rock (one formed by the cooling of molten materials). See more »

  • Bentonite


    Bentonite, the name given to a group of industrially useful clays containing the mineral montmorillonite. See more »

  • Chalk


    Chalk, a very soft, powdery variety of limestone. Like all limestone, it consists mainly of calcium carbonate. See more »

  • Clay


    Clay, an earthy material composed of very small particles of weathered rock. The particles are less than 0.00015 inch (0.004 mm) in diameter, much smaller than sand particles. See more »

  • Conglomerate (geology)

    Conglomerate (geology)

    Conglomerate, in geology, a sedimentary rock composed of rounded rock fragments cemented together by a finer-grained material such as sand or clay. See more »

  • 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 »

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