A series of amphiboles ranging from pure magnesium to iron-rich compositions. The more iron, the deeper the color (A).
Actinolite is a very common amphibole in medium-grade metamorphic rocks. It is pleochroic in shades of light green, with moderate relief. Often shows good 56-124 degree amphibole cleavage (C).
Tremolite occurs in magnesium-rich settings like metamorphosed, impure dolomites. It is like actinolite in properties but colorless (B).
Mostly first-order interference colors, sometimes second order, not too much affected by the generally light color.
Below is tremolite in thin section. The high-relief material is tremolite (actually, some of the relief is highly negative since the surrounding material is calcite). The large grain in the center of the field shows the 56-124 amphibole cleavage.
Same field in crossed polars. Note the typical second-order interference colors and the 56-124 cleavage.
Created 10 Oct 1997, Last Update 14 Dec 2009
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