Labradorite

Formula:  Na_0.5-0.3Ca_0.5-0.7Al_1.5-1.7Si_2.5-2.3O₈

Origin of name:  After locality; Island off Labrador, Canada

Crystal system:  Triclinic

Crystal class:  -1

Twinning:  Common by pericline, Carlsbad, Baveno, or Manebach law

Unit cell: a = 8.16 Ǻ, b = 12.86 Ǻ, c = 7.10 Ǻ, α = 90.5°, β = 116.1°, γ = 89.8°

Colour:  Colourless, white, gray; frequently shows play of colours

Diaphaneity: 

Luster:  Vitreous

Habit:  Crystals tabular; massive, cleavable, granular or compact

Hardness:  6 to 6.5

Specific gravity:  2.69 to 2.72

Cleavage:  3; {001} perfect, {010} and {110} nearly perfect

Tenacity: 

Streak: 

Synonyms/varieties:  Plagioclase [An 50=70]

Comments:  Intermediate member of plagioclase series