Bytownite

Formula:  (Ca_xNa_1-x)(Si_3-xAl_1+x)₄O₈    (x= 0.7 - 0.9)

Origin of name:  Locality; Bytown (now Ottawa), Ontario, Canada

Crystal system:  Triclinic

Crystal class: 1

Twinning:  Common by albite law; also by Carlsbad or pericline law

Unit cell: a = 8.18 Ǻ, b = 12.87 Ǻ, c = 14.19 Ǻ, α = 93.5°, β = 115.9°, γ = 90.6°

Colour:  Colourless, white, gray

Diaphaneity: Translucent to transparent

Luster:  Vitreous

Habit:  Crystals tabular; massive, granular

Hardness:  6 to 6.5

Specific gravity:  2.72 to 2.74

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

Tenacity:  Conchoidal to uneven; brittle

Streak:  White

Synonyms/varieties:  Plagioclase [An 70-90]

Comments:  Intermediate member of plagioclase series