| Brownmillerite | |
|---|---|
 Red/red-brown crystals of brownmillerite from Caspar quarry, Bellerberg Volcano, Ettringen, Mayen, Eifel Mts, Rhineland-Palatinate, Germany | |
| General | |
| Category | Oxide mineral |
| Formula (repeating unit) | Ca2(Al,Fe)2O5 |
| IMA symbol | Bmlr[1] |
| Strunz classification | 4.AC.10 |
| Dana classification | 7.11.2.1 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Ibm2 |
| Unit cell | a = 5.57 Å, b = 14.52 Å, c = 5.34 Å; Z = 4 |
| Identification | |
| Color | Reddish brown |
| Crystal habit | As minute square platelets; massive |
| Diaphaneity | Semitransparent |
| Specific gravity | 3.76 |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.960 nβ = 2.010 nγ = 2.040 |
| Birefringence | δ = 0.080 |
| Pleochroism | Distinct; X = Y = yellow-brown; Z = dark brown |
| 2V angle | 75° (measured) |
| References | [2][3][4][5] |
Brownmillerite is a rare oxide mineral with chemical formula Ca2(Al,Fe)2O5. It is named for Lorrin Thomas Brownmiller (1902–1990), chief chemist of the Alpha Portland Cement Company, Easton, Pennsylvania.
- ^ 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
- ^ Handbook of Mineralogy – Brownmillerite
- ^ Mindat.org – Brownmillerite
- ^ Brownmillerite data on Webmineral.com