Chalcanthite

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Chalcanthite
General
Category	Sulfate mineral
Formula (repeating unit)	CuSO4·5H2O
IMA symbol	Cct[1]
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
2V angle	Measured: 56°
Solubility	Soluble in water, turning it blue
Other characteristics	Poisonous
References	[2][3][4]

Chalcanthite (from Ancient Greek χάλκανθον (khálkanthon), from χαλκός (khalkós) 'copper', and ἄνθος (ánthos) 'flower, bloom') is a richly colored blue-green water-soluble sulfate mineral CuSO₄·5H₂O. It is commonly found in the late-stage oxidation zones of copper deposits. Due to its ready solubility, chalcanthite is more common in arid regions.

Chalcanthite is a pentahydrate and the most common member of a group of similar hydrated sulfates, the chalcanthite group. These other sulfates are identical in chemical composition to chalcanthite, with the exception of replacement of the copper ion by either manganese as jokokuite, iron as melanterite, or magnesium as pentahydrite.^[5]

Other names include blue stone, blue vitriol, and copper vitriol.^[3]