Tourmaline Group Na-Fe-Mg-Li Al borosilicates

Optical Properties:

Uniaxial -; parallel extinction; color varies from colorless to pale yellow, pink green, blue, etc., depending on variety; color zoning is common; moderate birefringence, typically second order colors.

The photos above, under crossed polarizers, show tourmaline with quartz inclusions and surrounded by quartz (left picture), and zoned tourmaline crystals surrounded by muscovite in the picture on the right.

Occurrence:

Large crystals are found in granite pegmatites. Other occurrences are in high temperature veins, schists, and gneisses.

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