Amphibole discrimination tutorial Optical mineralogy

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)