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Archean of, relating to, or designating the earlier of two geological periods of the Precambrian Era, ending approximately 2.5 billion years ago, during which highly crystalline igneous and metamorphic rocks were formed; Early Precambrian; Archeozoic; azoic. [1/2 definitions]
biotite a mica commonly found in igneous and metamorphic rock, ranging in color from dark green or brown to black, and containing iron, magnesium, potassium, and aluminum.
gneiss a metamorphic rock made up of minerals similar to those in granite but arranged in bands that differ in color, some bands containing feldspar and quartz and others containing hornblende and mica.
hornblende a variety of amphibole that is greenish to black in color, common in metamorphic rocks and dark igneous rocks that are rich in iron and magnesium.
marble a metamorphic form of limestone, found in many colors and varieties, that can be cut and polished to a hard, shiny surface. [1/7 definitions]
olivine a common mineral silicate of magnesium and iron, found in gray-green crystalline masses in igneous and metamorphic rock, and used esp. as a structural material in bricks for lining furnaces.
quartzite a metamorphic rock that consists of quartz and hardened sandstone.
schist any of several metamorphic rocks made up of thin, roughly parallel mineral layers that split easily.
slate a fine-grained, metamorphic rock that tends to split in smooth layers. [1/6 definitions]