Trachyte is an igneous volcanic rock with an aphanitic to porphyritic texture. It is the volcanic equivalent of syenite. The mineral assemblage consists of essential alkali feldspar; relatively minor plagioclase and quartz or a feldspathoid such as nepheline may also be present. (See the QAPF diagram). Biotite, clinopyroxene and olivine are common...
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http://en.wikipedia.org/wiki/Trachyte
A group of fine-grained, generally porphyritic, extrusive igneous rocks having alkali feldspar and minor mafic minerals as the main components, and possibly a small amount of sodic plagioclase.
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• (n.) An igneous rock, usually light gray in color and breaking with a rough surface. It consists chiefly of orthoclase feldspar with sometimes hornblende and mica.
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A group of fine-grained, generally porphyritic, extrusive igneous rocks having alkali feldspar and minor mafic minerals as the main components, and possibly a small amount of sodic plagioclase.
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http://volcano.oregonstate.edu/glossary/1
light-coloured, very fine-grained extrusive igneous rock that is composed chiefly of alkali feldspar with minor amounts of dark-coloured minerals ... [1 related articles]
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http://www.britannica.com/eb/a-z/t/68
A group of fine-grained, generally porphyritic, extrusive igneous rocks having alkali feldspar and minor mafic minerals as the main components, and possibly a small amount of sodic plagioclase.
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http://www.encyclo.co.uk/local/21455
A fine-grained volcanic rock that contains large amounts of potassium feldspar.
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Trachyte is a group of igneous volcanic rocks, grey, yellow, brown, green and red in colour consisting chiefly of alkali feldspar, and often containing crystals of glassy feldspar, mica, hornblende, or augite. Trachyte occurs in lava, intrusive sheets, and dykes from the early Tertiary period. It is sometimes used as a paving material.
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