White crystal group de the extremely rare Al phosphate sulphate mineral sanjuanite from the type locality and only one of the two known localities worldwide: Sierra Chica de Zonda, Pocito Department, San Juan, Argentina. Ex Vandenbroucke Museum collection specimen, from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Sanjuanite
Sanjuanite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Al₂(PO₄)(SO₄)(OH)·9H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/n).
Key properties: Mohs hardness 3; specific gravity 1.94; Dull to silky luster; optically biaxial.
IMA symbol Sjn, IMA status: approved, named in 1966.
Found in mineralized joint fractures cutting slate.
It is found associated with Gypsum, natrojarosite, iron oxides.
The name refers to San Juan Province, Argentina, in which the mineral was first found.