Tourmaline
October's Birthstone

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CHEMISTRY Elbaite, Na(Li,Al)₃Al₆B₃Si₆O₂₇(OH)₃(OH,F)
CRYSTALLOGRAPHY Hexagonal
REFRACTIVE INDEX 1.603 - 1.655
HARDNESS 7 - 7.5
SPECIFIC GRAVITY 2.84 - 3.10
CLEAVAGE No
HEAT SENSITIVE Some

WEARABILITY* Very Good
SPECIAL CARE INSTRUCTIONS Multicolored gems are often weak where the colors meet

ENHANCEMENTS Heat treatment, common on dark gems, otherwise occasional. Irridation, occasional.

*Wearability is graded as Excellent, Very Good, Good, Poor, and Forget It!
For more details see the article on "Hardness and Wearability."

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