sillimanite

{{Infobox mineral | name = Sillimanite | category = Nesosilicate | boxwidth = | image = Sillimanite-k302a.jpg | alt = | caption = | formula = Al2SiO5 | IMAsymbol = Sil | molweight = | strunz = 9.AF.05 | dana = 52.02.02a.01 | system = Orthorhombic | class = Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) | symmetry = Pbnm | unit cell = a = 7.47 Å, b = 7.66 Å c = 5.75 Å; Z = 4 | color = Colourless or white to grey, also brown, yellow, yellow-green, grey-green, blue-green, blue; colourless in thin section | colour = | habit = Prismatic crystals, fibrous, acicular | twinning = | cleavage = {010} perfect | fracture = Splintery | tenacity = Tough | mohs = 7 | luster = Vitreous to subadamantine, silky | streak = White | diaphaneity = Transparent to translucent | gravity = 3.24 | density = | polish = | opticalprop = Biaxial (+) | refractive = nα = 1.653 – 1.661 nβ = 1.654 – 1.670 nγ = 1.669 – 1.684 | birefringence = δ = 0.020 – 0.022 | pleochroism = Colourless to pale brown to yellow | 2V = 21–30° | dispersion = | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = | alteration = | references = }}

Sillimanite or fibrolite is an aluminosilicate mineral with the chemical formula Al2SiO5. Sillimanite is named after the American chemist Benjamin Silliman (1779–1864). It was first described in 1824 for an occurrence in Chester, Connecticut.