Lawsonite H4CaAl2Si2O10

Optical Properties:

Biaxial +; 2V>80 degrees; colorless; interference colors to second order; polysynthetic twinning is apparent is some grains; two good cleavages. Both of the photos above are under crossed polarizers. In the photo on the left, polysynthetic twins are apparent; on the right, various interference colors of lawsonite are shown.

Occurrence:

Lawsonite is an indicator mineral of blueschist grade metamorphism (high pressure, low temperature metamorphism). It is associated with white mica, glaucophane, epidote, chlorite, albite, quartz, and occasionally jadeite and aragonite.

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