crystals of sapphirine, crystals of mica var. muscovite : Betroka District, Anosy Region (Fort Dauphin Region), Tuléar Province (Toliara), Madagascar — Photo: Parent Géry · CC BY-SA 3.0
Sapphirine
A rare magnesium-aluminium silicate named for its sapphire-like blue — a collector's gem of high-grade metamorphic rocks.
Intro adapted from Wikipedia (CC BY-SA).
Sapphirine is an IMA-recognized mineral species in the silicate class, with the chemical formula Mg₄(Mg₃Al₉)O₄[Si₃Al₉O₃₆].
It crystallizes in the monoclinic crystal system (space group P-1). It is a member of the Sapphirine structural group.
Key properties: Mohs hardness 7.5; specific gravity 3.4–3.58; typically blue or green; white streak; Vitreous luster; refractive index 1.717; optically biaxial.
IMA symbol Spr, grandfathered status — known before the IMA’s founding, named in 1819.
Found in high-temperature metamorphic rocks or xenoliths with abundant aluminum and magnesium and low silicon. can occur as a primary magmatic mineral in subsilicic rocks.
It is found associated with Sillimanite, kyanite, cordierite, kornerupine, corundum, surinamite, phlogopite, chrysoberyl, pyroxenes, spinel, garnet, calcite, quartz.
The name refers to its typical sapphire-blue color.
Collections: Gemstones, Rare & Remarkable.