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Labradorite (Silicate-Tectosilicate) 

(Ca,Na)(Al,Si)Si2O8

Hardness: 6.0 - 6.5
Specific Gravity: 2.70 - 2.74

Characteristics: Belongs to plagioclase feldspar series; labradorite by definition must contain 50-70% Ca to 50-30% Na; gray to smoky black; features labradorescence, a play of colors as shown in the photograph to the right; dull to vitreous luster; transparent to translucent; perfect cleavage in one direction, good in another; conchoidal fracture.

Found in gabbros, mafic igneous rocks of low silica content, and anorthosites. Associated minerals include biotite, pyroxene, and hornblende.

Labradorite is primarily used as an ornamental and semi-precious stone.(Primary text: Perkins, D. 2002. Mineralogy. Prentice Hall.)

 
 

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