Tremolite-Actinolite Ca2(Mg,Fe)5(OH)2(Si4O11)2

Optical Properties:

Biaxial -; colorless to pale green in plane polarized light; amphibole cleavage (2 directions at 56 degrees); interference colors up to middle second order; inclined extinction; prismatic to fibrous form.

The photo above, under crossed polarizers, shows the moderate birefringence and cleavage of tremolite. The pictures below (crossed polarizers on the left, plane polarized light on the right) show a tremolite schist, composed almost entirely of tremolite. Interlocking fibers of tremolite form the jade mineral, nephrite.

Occurrence:

Common in contact metamorphosed carbonate rocks; the Fe-rich member, actinolite, occurs in metamorphosed mafic rocks.

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