Mineral - Anorthite
Anorthite
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
CaAl₂Si₂O₈
Unit Cell
a=8.18 b=12.88 c=14.17 α=93° β=116° γ=92° Z=8
Physical Properties
Hardness
6 - 6.5
Streak
white
Density
Normal (2-3,5)
Cleavage
Perfect after {001}, indistinct after {010}, imperfect after {110}
Fracture
conchoidal,
uneven
Tenacity
Brittle
Optical Properties
Color
whitegrayredorange
Birefringence
0.012
Luster
Vitreous
Transparency
translucent,
transparent
Pleochroism
Geomineralogical Properties
Crystal System
triclinic
Point Group
triclinic-pinacoidal - 1
Space Group
P 1 (2)
Habit
granular, prismatic
Formation
Igneous, in mafic plutonites and volcanic rocks
In granulite-facies metamorphites and carbonatites
Paragenesis
Twinning
Rarity
Common
Synonyms
Anorthite, Andesine, Oligoclase, Bytownite, Labradorite
Composition
Elements
Mass
SiO₂
45.88
TiO₂
0.04
Al₂O₃
34.31
Fe₂O₃
0.83
CaO
18.28
Na₂O
0.82
K₂O
0.11
H₂O
0.14
England (Dana 1892)
Groups and Members
Feldspar-Group
Plagioclase-Subgroup
Name and first discovery : Named in 1823 by Gustav Rose after the Greek word "anorthosi" for "not right-angled" due to its triclinic symmetry.
Chemistry : Polymorph after Dmisteinbergite, Stöfflerite and Svyatoslavite
Synonyms : Amphodelite, Barsovite, Beffanite, Biotin, Claciklase, Christianite, Latropite
Varieties : Bytownite, Labradorite
Abbreviation: An
literature
Dana, J. D., & Dana, E. S. (1892). The system of mineralogy of James Dwight Dana, 1837-1868: descriptive mineralogy . J. Wiley & sons.