GEO 2163 Lecture Notes - Lecture 5: Crystal Habit, Titanite, Apatite
13 May 2018
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Lab 2: Retardation, Birefringence, Sign of Elongation, Extinction
1-E (from lab 1):
In this thin section sample (2162-2) there were five
minerals that have been observed.
First was the alkali feldspar. It appeared transparent to
translucent light grey with an anhedral mineral habit.
Its absorption color was white/colorless to light grey.
No cleavage was observed, and it has a low negative
relief. Within this feldspar, straight lines were
observed and rippley-like textures/braided textures
have been observed, as a result of ex-solution.
Plagioclase twinning was observed.
The second mineral observed was the green amphibole
which was green translucent and had anhedral,
elongated mineral habit. Its absorption color was green
and two cleavage planes were observed that
intersected at about 60 degrees and 120 degrees. This
mineral has a moderate to high positive relief.
Lamellar twinning was also observed.
The third mineral to be studied within this thin section
was the brown biotite, which was a translucent
brown/black mineral. It showed anhedral mineral habit
and its absorption color was brown and black, it
changes when stage is rotated due to basal cleavages,
which was also noted. It has a moderately high positive
relief. And no other textures or twinning was observed
in this mineral.
The fourth mineral to be observed in this sample was
the trace amounts of titanite, which was a translucent
brown-grey mineral. It displayed an anhedral mineral
habit with an absorption color of grey to pale brown.
No cleavage was observed; it has a very high positive
relief.
The fifth and last mineral in the thin section to be
observed was the apatite, which was a translucent
white/colorless mineral. It showed a subhedral to
euhedral mineral habit with round edges and some
crystals appeared elongated. Its absorption color was
white/colorless. No cleavage was observed in this thin
section. This apatite has a moderately high positive
relief. Some other textures observed were the
diagnostic hexagonal outline and nicely rounded-
edges outline. No twinning observed.
Relative abundancies of these minerals in this thin
section are estimated to be:
50% alkali feldspar, 25% green amphibole, 15%
brown biotite, 7% apatite, 3% trace titanite
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Document Summary
Lab 2: retardation, birefringence, sign of elongation, extinction relief. And no other textures or twinning was observed in this mineral. The fourth mineral to be observed in this sample was the trace amounts of titanite, which was a translucent brown-grey mineral. It displayed an anhedral mineral habit with an absorption color of grey to pale brown. No cleavage was observed; it has a very high positive relief. The fifth and last mineral in the thin section to be observed was the apatite, which was a translucent white/colorless mineral. It showed a subhedral to euhedral mineral habit with round edges and some crystals appeared elongated. No cleavage was observed in this thin section. This apatite has a moderately high positive relief. Some other the diagnostic hexagonal outline and nicely rounded- edges outline. Relative abundancies of these minerals in this thin section are estimated to be:
