Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
A somewhat uncommon mineral but very important geologically because it is pretty much confined to high-pressure, low temperature subduction zone settings. Thus it is of great tectonic significance. It's a sodium-bearing amphibole.
Moderate relief, pleochroic in shades from near colorless through light blue to lavender. The color is the most distinctive feature.
Moderate birefringence, resulting in first- and second-order colors that are not too badly modified by its natural color.
The light blue and purplish mineral with low relief below is glaucophane, seen in plane-polarized light.
The same filed in crossed polarizers. The light coloring of glaucophane has little effect on its interference colors.
Created 10 Oct 1997, Last Update 10 Oct 1997
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