Plagioclase series

Formula: (Ca_xNa_1-x)(Si_3-xAl_1+x)O₈ (x = 0-1)

Origin of name: from Greek plagios = oblique and klas = to cleave

Crystal system: triclinic

Crystal class: -1

Twinning: 

Unit cell: 

Colour: usually colourless, white or gray, also yellow, bluish, reddish, greenish

Diaphaneity: transparent to translucent

Luster: vitreous

Habit: crystals tabular, also prismatic or equant, commonly twinned, massive, cleavable, granular or compact

Hardness: 6 to 6.5

Specific gravity: 2.62 to 2.76

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

Tenacity: 

Streak: colourless

Synonyms/varieties:

Comments: there are six members of the plagioclase series defined by their contents of Na and Ca: albite (x = 0-0.1), oligoclase (x = 0.1-0.3), andesine (x = 0.3-0.5), labradorite (x = 0.5-0.7), bytownite (x = 0.7-0.9) and anorthite (x = 0.9-1.0)