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Trolleite
Trolleite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Al₄(PO₄)₃(OH)₃.
It crystallizes in the monoclinic crystal system (space group I2/c).
Key properties: Mohs hardness 8.5; specific gravity 3.1; Vitreous luster; optically biaxial.
IMA symbol Tll, grandfathered status — known before the IMA’s founding, named in 1868.
Found in amphibolite-grade metamorphic rocks.
It is found associated with Berlinite, attakolite, augelite, lazulite (Västanå mine, Sweden); scorzalite, augelite, viséite (Champion mine, California, USA); montebrasite, scorzalite.
The mineral was named to honor Hans Gabriel Trolle-Wachtmeister (1782–1871), Swedish chemist.