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Trachyte
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 accessory minerals.
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