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Trachyte |
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trachyteLight-coloured, very fine-grained igneous rock composed chiefly of alkali feldspar with only minor mafic minerals (biotite, hornblende, or pyroxene). Trachyte is commonly found in volcanic regions; like many volcanic rocks, it shows a streaked or banded structure due to flowing of the congealing lava. trachyte [′tra‚kīt] (petrology) The light-colored, aphanitic rock (the volcanic equivalent of syenite), composed largely of alkali feldspar with minor amounts of mafic minerals. Trachyte a cenotypal extrusive, usually porphyritic rock. Porphyritic phenocrysts and microlites embedded in volcanic glass are represented by sanidine; neutral and acid plagioclase, biotite, pyroxene, or amphibole are encountered in lesser amounts. Trachyte is the extrusive equivalent of syenite. It consists of up to 60 percent silica and up to 10 percent alkalies. The rock is rough to the touch. There are glassy trachytes, such as obsidians and pumices, and trachytic tuffs. Trachytes grade into liparites, andesites, and basalts. They are found in the Caucasus and, outside the USSR, in Italy and France. Trachyte is a relatively rare rock. (See also.) Want to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit the webmaster's page for free fun content. |
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