K-feldspar tutorial Optical mineralogy
Channel: Matt Kohn
Date: 2021-05-03

Several videos of K-feldspar in thin section, showing typical textures and optical characteristics. Supported by Boise State University and the US National Science Foundation.
Key characteristics: Relief very slightly lower than quartz (subtle), clear in plane-polarized light, with no pleochroism, low interference colors (white), tartan twinning (microcline), perthite (albite exsolution), carlsbad twinning (sanidine), clay alteration (brown "staining").
00:00​ Typical microcline with tartan twinning
00:30​ More tartan twinning
01:00​ Slightly perthitic
01:31​ Strongly perthitic, clay alteration
02:01​ Beautiful perthite, clay alteration
02:31​ Sanidine