A biotite granite, sample 69MW1518 has a
composition of plagioclase (35%), K-feldspar (30%), quartz (20%),
biotite (10%), sericite (3%), sphene (1%), and trace hornblende,
muscovite, chlorite, oxides, and epidote. Seritized plagioclase
porphyries (up to 7 mm), show albite twinning. K-feldspar porphyries
exhibit undulose extinction, minor perthite, carlsbad and tartan
twinning, and plagioclase inclusions. Quartz occurs as recrystallized
grains with 120º grain boundaries in mm-thick equigranular domains.
Biotite occurs in clusters with no preferred orientation, and is in some
places replaced by chlorite. Hornblende is deep brown and rimmed by
epidote, plagioclase and biotite. Sphene occurs as subhedral,
rhomb-shaped grains that are visible in hand sample. No fabric is
recognized in this granite.