Albite

Formula: (Ca_xNa_1-x)(Si_3-xAl_1+x)₄O₈     (x= 0.0 - 0.1)

Origin of name:  From Latin, albus - white

Crystal system:  Triclinic

Crystal class:  -1

Twinning:  Very common by albite law; common by pericline law; also by Carlsbad, Baveno, or Manebach law

Unit cell:  a = 8.14 Å, b = 12.79 Å, c = 7.16 Å, a = 94.3°, b = 116.6°, g = 87.7°

Colour:  White to colourless, bluish, gray, reddish, greenish

Diaphaneity: Transparent to translucent

Luster:  Vitreous, pearly on cleavages

Habit:  Crystals tabular, small; usually massive, lamellar, or granular

Hardness:  6 to 6.5

Specific gravity:  2.60 to 2.63

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

Tenacity:  Brittle

Streak:  White

Synonyms/varieties:  Cleavelandite (platy var.), soda feldspar, sodium feldspar, plagioclase [An 0-10]

Comments:  Series with anorthite (plagioclase series) and with microcline. A major constituent of granites and granite pegmatites, alkalic diorites, basalts and in hydrothermal and alpine veins. A product of potassium metasomatism and in low-temperature and low-pressure metamorphic facies and in some schists. Detrital and authigenic in sedimentary rocks.