Creedite

Creedite is a calcium aluminium sulfate fluoro hydroxide mineral with formula: Ca₃Al₂SO₄(F,OH)₁₀·2(H₂O). Creedite forms colorless to white to purple monoclinic prismatic crystals. It often occurs as acicular radiating sprays of fine prisms. It is translucent to transparent with indices of refraction of n_α = 1.461 n_β = 1.478 n_γ = 1.485. It has a Mohs hardness of 3.5 to 4 and a specific gravity of 2.7.