PETROLOGY TERMS

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.
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Gneiss

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

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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

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

  • Basalt

    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

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

  • Chalk

    Chalk

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

  • Clay

    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

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

  • Diatomite

    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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