Celsian | |
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![]() Celsian (transparent/gray in photo) in sanbornite (white) and quartz matrix from Incline, Maricopa County, California (Size: 5 x 4 x 3 cm) | |
General | |
Category | Feldspar |
Formula (repeating unit) | BaAl2Si2O8 |
IMA symbol | Cls[1] |
Strunz classification | 9.FA.30 |
Crystal system | Monoclinic |
Crystal class | Prismatic (2/m) (same H-M symbol) |
Space group | I2/c |
Unit cell | a = 8.622(4) Å, b = 13.078(6) Å, c = 14.411(8) Å; β = 115.2°; Z = 8 |
Identification | |
Color | Colorless, white, yellow |
Crystal habit | Short prismatic to acicular crystals, massive |
Twinning | Manebach twins on (001), baveno twins (021), rare lamellar twinning |
Cleavage | Perfect on {001}, good on {010}, poor on {110} |
Tenacity | Brittle |
Mohs scale hardness | 6–6.5 |
Luster | Vitreous |
Diaphaneity | Transparent |
Specific gravity | 3.10 to 3.39 |
Optical properties | Biaxial (+) |
Refractive index | nα = 1.580–1.584 nβ = 1.585–1.587 nγ = 1.594–1.596 |
Birefringence | 0.014, biaxial – |
2V angle | Measured: 86° to 90° |
Other characteristics | [2][3][4][5] |
Celsian is an uncommon feldspar mineral, barium aluminosilicate, BaAl2Si2O8. The mineral occurs in contact metamorphic rocks with significant barium content. Its crystal system is monoclinic, and it is white, yellow, or transparent in appearance. In pure form, it is transparent. Synthetic barium aluminosilicate is used as a ceramic in dental fillings and other applications.
The mineral is named after Anders Celsius (1701–1744).