Copiapite

Copiapite
Copiapite from the Bolesław Mine, Kłodzko District, Lower Silesia, Poland
General
Category	Sulfate minerals
Formula (repeating unit)	${\ce {Fe^{2+}Fe^{3+}4(SO4)6(OH)2.20H2O}}$
Strunz classification	7.DB.35
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Unit cell	a = 7.337 Å, b = 18.76 Å, c = 7.379 Å; α = 91.47°, β = 102.18°, γ = 98.95°; Z = 1
Identification
Color	Sulfur-yellow to orange when crystalline, greenish-yellow to olive-green when massive
Crystal habit	Tabular pseudo-orthorhombic platy crystals, typically in scaly incrustations or granular pulverulent aggregates
Twinning	Contact twins
Cleavage	Perfect on {010}, imperfect on {101}
Fracture	Irregular/uneven, micaceous
Tenacity	Fragile
Mohs scale hardness	2.5 - 3
Luster	Pearly on {010}
Diaphaneity	Transparent to translucent
Specific gravity	2.04–2.17
Optical properties	Biaxial (+)
Refractive index	n_α = 1.506 - 1.540 n_β = 1.528 - 1.549 n_γ = 1.575 - 1.600
Birefringence	δ = 0.069
Pleochroism	X = Y = pale yellow to colorless; Z = sulfur-yellow
2V angle	Measured: 45° to 74°, Calculated: 48° to 72°
Solubility	Soluble in water
References

Copiapite is a hydrated iron sulfate mineral with formula: ${\ce {Fe^{2+}Fe^{3+}4(SO4)6(OH)2.20H2O}}$ Copiapite can also refer to a mineral group, the copiapite group.

Copiapite is strictly a secondary mineral forming from the weathering or oxidation of iron sulfide minerals or sulfide-rich coal. Its most common occurrence is as the end member mineral from the rapid oxidation of pyrite. It also occurs rarely with fumaroles. It occurs with melanterite, alunogen, fibroferrite, halotrichite, botryogen, butlerite and amarantite. It is by far the most common mineral in the copiapite group.

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