Wardite

Wardite is a hydrous sodium aluminium phosphate hydroxide mineral with formula: NaAl₃(PO₄)₂(OH)₄·2(H₂O). Wardite is of interest for its rare crystallography. It crystallizes in the tetragonal trapezohedral class and is one of only a few minerals in that class. Wardite forms vitreous green to bluish green to white to colorless crystals, masses, and fibrous encrustations. It has a Mohs hardness of 5 and a specific gravity of 2.81–2.87.