Rating
Name	Microcline (thin section)
Type	Mineral
Cleavage	perfect cleavage; usually not observed in thin section
Colour and Pleochroism	Usually colorless, pale coloration possible in strongly colored samples.
Relief	Low negative relief
Form	Occurs as anhedral to euhedral grains, commonly displays a tabular or lathlike habit.
Optical Orientation	Inclined extinction, however twinning causes extinction angle to be difficult to determine
Twinning	Simple and tartan twinning common
Birefringence, δ	δ = 0.005 - 0.008; Maximum interference color first order grey to white
Optical Character	Biaxial (-)
2V	2Vx = 65 - 88°
Key Characteristics	The mineral's low relief, lack of color and tartan twinning are characteristic. In plagioclase feldspar polysynthetic twinning in two directions can mimic microcline's tartan twinning. However, the polysynthetic twinning of plagioclase is clearly defined and does not pinch and swell as the tartan twinning of microcline does.
Photograph Comments	pic 1(left): plane polarized light, magnification 40x; cross polarized light, magnification 40x, light horizontal bands which pinch and swell are exsolution lamellae of albite; tartan twinning not present in this picture
Hand Sample URL	http://digicon.athabascau.ca/u?/RM,74
Subject	Minerals; Rocks; Identification photographs; Geology;
Date	2009
Format	image/jpeg
Identifier	2009-rm-0009
Collection Title	Rock and Mineral Samples
Repository	AU Digital Library
Rights	Subject to the Copyright Act

Microcline (thin section)

Description