Labradorite is a feldspar mineral most often found in igneous rocks. Some specimens of labradorite exhibit a phenomenon is known as labradorescence, which is a strong play of iridescent blue, green, red, orange, and yellow colors.   Specimens with the highest quality labradorescence are often selected for use as gemstones.

Physical Properties of Labradorite

Color: Usually clear, white, or gray in reflected light. Labradorescent colors can include blue, green, yellow, orange, and red.
Streak: White
Luster: Vitreous, pearly on cleavage faces
Diaphaneity: Transparent to translucent
Cleavage: Two directions of perfect cleavage intersecting at about 86 degrees
Mohs Hardness: 6 to 6.5
Specific Gravity: 2.68 to 2.72
Diagnostic Properties: Hardness, cleavage (twinning and labradorescence are only shown by some specimens)
Chemical Composition: (Na,Ca)(Al,Si)4O8 with Na (30-50%) and Ca (70-50%)
Crystal System: Triclinic

Pictures of Labradorite specimen from recent Mobile Rock & Gem Annual Shows:

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