Edgrewite
Edgrewite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₉(SiO₄)₄F₂.
It crystallizes in the monoclinic crystal system (space group P2_1/b). It is a member of the Humite structural group.
Key properties: Mohs hardness 6.5; specific gravity 2.918; White streak; Vitreous luster; optically biaxial.
IMA symbol Egr, IMA status: approved, named in 2011.
Found in xenoliths of carbonate-silicate rock altered to sanidinite facies metamorphic rock within ignimbrites.
It is found associated with Bultfonteinite, hillebrandite, jennite, chegemite, larnite, rondorfite, hydroxylellestadite.
The mineral was named to honor Edward S. Grew (b. 1944), professor of mineralogy and petrology at the University of Maine, Orono, Maine, USA.