Cummingtonite tutorial Optical mineralogy
Channel: Matt Kohn
Date: 04/05/2021

Three videos of cummingtonite (Fe-Mg clinoamphibole) in thin section, showing typical textures and optical characteristics. Supported by Boise State University and the US National Science Foundation.
Key characteristics: moderate relief, colorless (maybe tan), amphibole cleavage (60°-120°), low interference colors, twins.
00:00​ Typical, lots of twins. Any apparent pleochroism = optical abberation
00:30 Together with hornblende
01:01 Hornblende core overgrown by cummingtonite