Page 75 - Petrology of Sedimentary Rocks

Genetic Classification of Quartz Types
(After P. D. Krynine)

e 1
c axis
I
V Perfect crystal
0
COMMON (PLUTONIC) in 3-D view.
1. Straight to slightly undu- n No prism faces.
lose extinction. @ 63
2. Some vacuoles; may be a VOLCANIC
few micro1 i tes 1. ldiomorphic hexagonal-bipyramidal shape
3. Subequant, xenomorphic with perfectly straight sides and rounded
4. Typical of granites; but corners. Prism faces very small or lacking.
also furnished by many Embaymen t s common.
other sources. 2. Almost no inclusions; water-clear. May
have negative crystals (n).
3. Straight extinction.

\
0’ ’ \
‘. .
@
RECRYSTALLIZED METAMORPHIC
1. Straight boundaries between
VEIN
equant interlocking grains,
1. Abundant vacuoles; sometimes vermi-
cular chlorite (c); rarely, zoned forming mosaic.
phantom crystals (ph). 2. May be some microlites & vacuoles.
2. Semi-composite to straight or 3. Straight to slightly undulose
undulose extinction, some may be (Do extinction. confuse with quartz-cemented
not
badly sheared. Often shows
comb structure. sands ! )
3. Often forms lsarge grains and

STRETCHED METAMORPHIC
SCHISTOSE METAMORPHIC 1. Stronq undulose extinction; bor-
ders may be smooth (sm), crenulated
1. Elongate, composite with straiqht
borders. (cr) or granulated (gr).
2. Mica inclusions (m). 2. Elongate, lenticular shape of
3. Straight to slightly undulose crystal units.
extinction. 3. Some microlites and vacuoles.

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