| Mullite | |
|---|---|
 White, filamentous mullite in front of thicker osumilite platelets (Photo width 1.5 mm) Found in Wannenköpfe, Ochtendung, Eifel, Germany | |
| General | |
| Category | Nesosilicate |
| Formula (repeating unit) | Al6Si2O13 |
| IMA symbol | Mul[1] |
| Strunz classification | 9.AF.20 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Pbnm, Pnnm |
| Unit cell | a = 7.5785(6) Å, b = 7.6817(7) Å, c = 2.8864(3) Å; Z = 1 |
| Identification | |
| Color | Colorless to pale pink or grey |
| Crystal habit | Prismatic to acicular crystals |
| Cleavage | Good on [010] |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.642 - 1.653 nβ = 1.644 - 1.655 nγ = 1.654 - 1.679 |
| Birefringence | δ = 0.012 - 0.026 |
| 2V angle | Measured: 20° to 50° |
| References | [2][3][4][5] |
Mullite or porcelainite[6] is a rare silicate mineral formed during contact metamorphism of clay minerals. It can form two stoichiometric forms: 3Al2O32SiO2 or 2Al2O3 SiO2. Unusually, mullite has no charge-balancing cations present. As a result, there are three different aluminium sites: two distorted tetrahedral and one octahedral.
Mullite was first described in 1924 for an occurrence on the Isle of Mull, Scotland.[5] It occurs as argillaceous inclusions in volcanic rocks in the Isle of Mull, inclusions in sillimanite within a tonalite at Val Sissone, Italy and with emerylike rocks in Argyllshire, Scotland.[3]
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Mineralienatlas
- ^ a b http://rruff.geo.arizona.edu/doclib/hom/mullite.pdf Handbook of Mineralogy
- ^ http://www.mindat.org/min-2806.html Mindat
- ^ a b http://webmineral.com/data/Mullite.shtml Webmineral
- ^ Neuendorf, K.K.E.; Mehl, J.P. Jr.; Jackson, J.A., eds. (2005). Glossary of Geology (5th ed.). Alexandria, Virginia: American Geological Institute. p. 428. ISBN 978-0922152896.