Chalcanthite General Category Sulfate minerals Formula (repeating unit) CuSO4·5H2O Strunz classification 7.CB.20 Crystal system Triclinic Crystal class Pinacoidal (1) (same H-M symbol) Space group P1 Unit cell a = 6.11 Å, b = 10.673 Å, c = 5.95 Å; α = 97.58°, β = 107.17°, γ = 77.55°; Z = 2 Identification Color Berlin blue to sky-blue, greenish blue Crystal habit Typically stalactitic, encrusted, reniform or massive. Natural crystals are rare, but are short prismatic or tabular Twinning Rare as cruciform twins Cleavage Perfect on {110}; interrupted on {110} Fracture Conchoidal Mohs scale hardness 2.5 Luster Vitreous Streak White Diaphaneity Transparent to translucent Specific gravity 2.12 - 2.3 Optical properties Biaxial (-) Refractive index nα = 1.514 nβ = 1.537 nγ = 1.543 Birefringence δ = 0.029 Solubility Soluble in water, turning it blue Other characteristics Poisonous References [1][2][3]