ERS201H5 Lecture Notes - Lecture 8: Xpl, Kyanite, Calcite
Document Summary
Both feldspars can be present in metamorphic rocks: na-rich plagin metamorphic rocks below 500oc, more ca-rich plagat higher temps, k-spar at mod to high grade. Feldspathoids silica poor pseudo feldspars: a group of minerals which look similar to feldspars but occur in silica under- saturated magmas they cannot occur in rocks alongside quartz. Calcite & dolomite caco3and camg(co3: calcite crystals are well known for their double refraction very high birefringence, calcite in hand sample easily distinguished soft + reactive, dolomite is less reactive than calcite (still fizzes a little) Calcite under the microscope: as light travels in calcite the light is refracted and causes it to be retarted away, only mineral that reacts with acid. Ppl colourless; variable relief with rotation of the stage (high and low relief only seen in this mineral very unique) ; generally anhedral shape (because of recrystallization); cleavage (3 not at 90o) Xpl high birefringence (4thorder); twinning often easy to spot (even in ppl)
