Brushite
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Brushite is a phosphate mineral with the chemical formula CaHPO₄·2H₂O. Crystals of the pure compound belong to the monoclinic space group C2/c and are colorless. It is the phosphate analogue of the arsenate pharmacolite. Wikipedia
Crystal habit: Prismatic to tabular acicular crystals; typically powdery or earthy
Crystal system: Monoclinic
Formula (repeating unit): CaHPO4 · 2 H2O
Refractive index: nα = 1.539 – 1.540; nβ = 1.544 – 1.546; nγ = 1.551 – 1.552
Solubility: Readily in HCl