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.

Porphyry (rock)

Porphyry, any igneous rock consisting of large crystals in a mass of much smaller crystals.

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  • 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 »

  • Granite


    Granite, a coarse-grained rock widely distributed in the earth's crust. Granite is very hard and takes a beautiful polish. 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 »

  • Marble


    Marble, a snowy white or richly colored ornamental stone. Polishing brings out the handsome grain, network of delicate veins, and cloudy hues that give marble its special beauty. 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 »

  • Petrology


    Petrology, the study of rocks. Petrology is a major subdivision of geology and is divided into two main branches: petrography and petrogenesis. See more »

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