celsian

{{Infobox mineral | name = Celsian | category = Tectosilicate minerals | group = Feldspar group | boxwidth = | boxbgcolor = | image = Celsian in sanbornite004.jpg | imagesize = 260px | caption = Celsian (transparent/gray in photo) in sanbornite (white) and quartz matrix from Incline, Maricopa County, California (Size: 5 x 4 x 3 cm) | formula = BaAl2Si2O8 | IMAsymbol=Cls | IMAstatus = Grandfathered (1895) | strunz = 9.FA.30 | dana = 76.1.1.4 | system = Monoclinic | class = Prismatic (2/m) | symmetry = I2/c (no. 15) | unit cell = a = 8.622(4) Å, b = 13.078(6) Å, c = 14.411(8) Å; β = 115.2°; Z = 8 | color = Colorless, white, yellow | 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} | fracture = | tenacity = Brittle | mohs = 6–6.5 | luster = Vitreous | refractive = nα = 1.580–1.584 nβ = 1.585–1.587 nγ = 1.594–1.596 | opticalprop = Biaxial (+) | 2V = Measured: 86° to 90° | birefringence = 0.014, biaxial – | pleochroism = | streak = | gravity = 3.10 to 3.39 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent | references = }}

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.