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Trachyandesite
Trachyandesite
is an
extrusive
igneous
rock
with a composition between
trachyte
and
andesite
. It has little or no free
quartz
, but is dominated by alkali
feldspar
and sodic
plagioclase
along with one or more of the following
mafic
minerals
:
amphibole
,
biotite
or
pyroxene
. Small amounts of
nepheline
may be present and
apatite
is a common accessory mineral.
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