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Formula:   Na(LiAl)3Al6(BO3)   mineral photo

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Crystal:   Hexagonal  
Hardness:   7-7.5  
Spec. Gr.:   3.03-3.25  
Streak:   White  
Cleavage:   Very Indistinct  
Location:   Mesa Grande,
San Diego County,

Most tourmaline crystals occur in granite pegmatites with a vertically striated elongated form with rounded triangular cross sections. Tourmaline is frequently referred to as the rainbow gemstone. If occurs in all spectral colors. Color banding may parallel either the base, length or termination of the crystal. Some tourmaline colors have special names: blue "indicolite," red "rubellite," and black "schorl." Its terminations lack a center of symmetry. One end may be flat, while the other is a rhombohedron. Gem crystals are found in Brazil, Madagascar, and at Pala and Mesa Grande, San Diego County, California.

Bibliography: Alain, Eid, Minerals of the World, pg. 55.

Vanders, Iris, Mineral Recognition, 1967, pg. 285-286.

University of California, Santa Barbara—Department of Earth Science
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