Saturday, March 21, 2015

Quartz

Quartz in thin section

Chemical formulae:

SiO4





Property


Twinning

No
Extinction

Undulose
Colour

Colourless in ppl
Relief

Very low
Pleochroism

No
Habit

Tabular, Prismatic
Birefringence






In PPL quartz is barely different to Feldspar. Quartz is usually a little cleaner looking than K-Feldspar, which often has tiny grainy inclusions in it. (Sericite Alteration or fine grained Muscovite with High Alteration Colours) and Plagioclase usually has good cleavage visible in XPL and similar tiny grainy inclusions. (Which may be epidote.)

Quartz is often confused with K-Feldspar, Plagioclase, Nepheline and Cordierite. See here for a good outline of the differences





Quartz in Plain Polarised Light
Quartz crystal in plain polarised light



Quartz in Cross Polarised Light
Quartz crystal in cross polarised light



Quartz Extinct in Cross Polarised Light
Quartz crystal in cross polarised light undulate extinction


video

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