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countable and uncountable, plural trachytes
(geology) A pale igneous rock consisting mostly of potassium feldspar and plagioclase. quotations
The type of rock that results is often described as trachyte and contains abundant crystals of a different kind of alkali-rich feldspar, such as sanidine, rather than plagioclase.
2004, Richard Fortey, The Earth, Folio Society, published 2011, page 52