Labradorite (Silicate-Tectosilicate)
(Ca,Na)(Al,Si)Si2O8Hardness: 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.)