Microcline (thin section)

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. 2V: 2Vx = 65 - 88° Relief: Low negative relief Cleavage: perfect cleavage; usually not observed in thin section Colour and Plechroism: Usually colorless, pale coloration possible in strongly colored samples. Optical Orientation: Inclined extinction, however twinning causes extinction angle to be difficult to determine Twinning: Simple and tartan twinning common Optical character: Biaxial (-)