Trachyte
Trachyte is an
igneous, volcanic (
extrusive)
rock, with
aphanitic to
porphyritic texture. Mineral assembly is usually, alkali
feldspar and
plagioclase (in a ratio > 1:4).
Quartz is absent.
Biotite,
pyroxene and scarce
olivine are common accessory minerals.
See also: igneous rocks, list of rocks