EARTHSC 2K03 Final: LAB EXAM
25 Feb 2017
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Document Summary
Does not have cleavage, nor does it have any twinning. No pleochroism; quartz is clear in ppl. Uniaxial positive = with gypsum plate inserted, interference figure turns blue. Undulatory extinction: the grain is broken up into sub grains that go extinct at different times. First order white with a tinge of yellow in thin section (xpl) Tabular meaning it looks like a square, rectangle or is six-sided (thin, flat and wide) Colourless in ppl and grey/black in xpl. Birefringence is 0. 005 0. 007; coloured first order grey and white. There are cloudy patches on individual crystals in ppl. In the picture below, orthoclase is the large white mineral next to the tabular black plagioclase. Can range in colour from white to grey in xpl; birefringence is 0. 005 0. 008. Albite and pericline twins make a cross-hatch twinning pattern. Colourless to pale green or yellow in thin section when viewed in xpl.
