Tourmaline (Cyclosilicates)

Tourmaline complex borosilicate (Na, Ca)(Li, Mg, Al)(Al, Fe, Mn)6 - (BO3)3(Si6O18)(OH)4
green & pinks crystals (variety elbaite) in albite/quartz matrix (photo courtesy of Amethyst Galleries, Inc.)			slender black crystals (variety schorl) in mica matrix (photo courtesy of Amethyst Galleries, Inc.)

Diagnostic properties:

Color: varied (depending on ions present).
Streak: white.
Hardness: 7 to 7.5.
Specific Gravity: 3.0 to 3.25.
Luster: vitreous to resinous.
Fracture: conchoidal.
Transparency: transparent to translucent.
Other properties: characteristic rounded triangular cross section of crystals; crystals often striated.
Occurrence: common.
Crystal system: hexagonal.
Uses: Some colored and transparent varieties are sold as semi-precious stones. Also used in high-pressure gauges (because of its piezoelectric property).
Name: from turamali, as gems from Sri Lanka were once called.

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