Amphibole discrimination tutorial Optical mineralogy
Channel: Matt Kohn
Date: 2021-05-07

A series of videos illustrating how to identify different amphiboles. Supported by Boise State University and the US National Science Foundation.
Clinoamphiboles (inclined extinction)
     Hornblende: Strongly pleochroic (usually) in browns and greens
     Actinolite: Pale green pleochroic
     Tremolite: Colorless
     Cummingtonite: Colorless, commonly twinned, coexists with hornblende
Orthoamphiboles (parallel extinction)
     Gedrite: Gray pleochroic
     Anthophyllite: colorless
00:00 Amphibole cleavage (60-120°) in hornblende
00:15 Amphibole cleavage (60-120°) in gedrite
00:31 Amphibole cleavage (60-120°) in glaucophane
00:46 Clinopyroxene with pseudo 60-120° cleavage (oblique section)
01:02 Characteristic cpx end section cleavage with c. 90-90° cleavage
01:17 Intermediate cpx section with c. 80-100° cleavage
01:32 How to find an end section with 60-120° cleavage
02:20 Inclined extinction in hornblende
02:51 Inclined extinction in actinolite
03:22 Inclined extinction and twins in cummingtonite
03:52 Parallel extinction in gedrite
04:22 Parallel extinction in anthophyllite
04:52 Gray pleochroism in gedrite
05:22 Brown pleochroism in hornblende (Ti-rich)
05:53 Green-Bluegreen-Yellowgreen pleochroism in hornblende
06:23 Blue-Lavender-Yellowgreen pleochroism in glaucophane
06:54 Actinolite cores (light green) with hornblende rims (darker green)
07:24 Hornblende core (dark green) with cummingtonite rim (colorless)