Brownmillerite Locality: Caspar quarry, Bellerberg volcano, Ettringen, Mayen, Eifel Mts, Rhineland-Palatinate, Germany Red/red-brown crystals of Brownmillerite from the TL (analysed). Field of view 3 mm. Specimen and photo Leon Hupperichs. — Photo: Leon Hupperichs · CC BY-SA 3.0
Brownmillerite
A rare calcium aluminium-iron oxide named for Lorrin Brownmiller, chief chemist of the Alpha Portland Cement Company.
Intro adapted from Wikipedia (CC BY-SA).
Brownmillerite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Ca₂Fe³⁺AlO₅.
It crystallizes in the orthorhombic crystal system (space group I2mb). It is a member of the Perovskite, Brownmillerite structural group.
Key properties: specific gravity 3.76; refractive index 2.003; optically biaxial.
IMA symbol Bmlr, IMA status: approved, named in 1963.
Found in thermally metamorphosed limestone blocks included in volcanic rocks (near Mayen, Germany); in high-temperature, thermally metamorphosed, impure limestones (Hatrurim Formation, Israel).
It is found associated with Calcite, ettringite, wollastonite, larnite, mayenite, gehlenite, diopside, pyrrhotite, grossular, spinel, afwillite, jennite, portlandite.
The artificial compound was named for Dr. Lorrin Thomas Brownmiller (1902–), Chief Chemist of the Alpha Portland Cement Company, Easton, Pennsylvania, USA, in 1932.