Outstanding yellow crystal aggregates of the very rare uranium mineral triangulite in a contrasting matrix. From Rhyolite Ridge, Cave Springs, Esmeralda County, Nevada, United States of America. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Triangulite
Triangulite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Al₃(UO₂)₄(PO₄)₄(OH)₅·5H₂O.
It crystallizes in the triclinic crystal system.
Key properties: Mohs hardness 2–3; specific gravity 3.7; Vitreous luster; optically biaxial.
IMA symbol Tri, IMA status: approved, named in 1981.
A rare secondary species in the uraniferous oxidized zone of a complex zoned granite pegmatite.
It is found associated with Meta-autunite, furongite, phosphuranylite, ranunculite, beryl, zircon, columbite, feldspar, quartz.
The name refers to the typical triangular habit of the crystals.