Copiapite
Copiapite from the Bolesław Mine, Kłodzko District, Lower Silesia, Poland
General
CategorySulfate minerals
Formula
(repeating unit)		Fe2+Fe3+4(SO4)6(OH)2·20(H2O)
IMA symbolCpi[1]
Strunz classification7.DB.35
Crystal systemTriclinic
Crystal classPinacoidal (1)
(same H-M symbol)
Space groupP1
Unit cella = 7.337 Å, b = 18.76 Å,
c = 7.379 Å; α = 91.47°,
β = 102.18°, γ = 98.95°; Z = 1
Identification
ColorSulfur-yellow to orange when crystalline, greenish-yellow to olive-green when massive
Crystal habitTabular pseudo-orthorhombic platy crystals, typically in scaly incrustations or granular pulverulent aggregates
TwinningContact twins
CleavagePerfect on {010}, imperfect on {101}
FractureIrregular/uneven, micaceous
TenacityFragile
Mohs scale hardness2.5–3
LusterPearly on {010}
DiaphaneityTransparent to translucent
Specific gravity2.04–2.17
Optical propertiesBiaxial (+)
Refractive indexnα = 1.506 – 1.540 nβ = 1.528 – 1.549 nγ = 1.575 – 1.600
Birefringenceδ = 0.069
PleochroismX = Y = pale yellow to colorless; Z = sulfur-yellow
2V angleMeasured: 45° to 74°, Calculated: 48° to 72°
SolubilitySoluble in water
References[2][3][4][5]

Copiapite is a hydrated iron sulfate mineral with formula: Fe2+Fe3+4(SO4)6(OH)2·20(H2O).[3] 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.[3] It is by far the most common mineral in the copiapite group.

It rarely occurs as single crystals, is in the triclinic crystal system, and is pale to bright yellow. It is soluble in water, changing the water color to deep orange or orangish-red. In solution copiapite is very acidic. In high concentrations a negative pH can occur, as reported in waters draining from Richmond Mine at Iron Mountain, California.[4] Copiapite can easily be distinguished from native sulfur because it does not give off an odor when dissolved in water. It can be distinguished from similar appearing uranium minerals, such as carnotite, by its lack of radioactivity. The only way to differentiate between the minerals in the copiapite group is by X-ray diffraction.

Copiapite was first described in 1833 for an occurrence near Copiapó, Atacama, Chile.[5] It is sometimes known as yellow copperas. Other occurrences are in California, Nevada, and in the filled paleo sinkholes and caves of Missouri.

Lustrous, micaceous crystals of copiapite to 8 mm on matrix from the Alcaparrosa Mine, El Loa Province, Antofagasta Region, Chile (sample size: 11.9 × 7.4 × 4.0 cm)

See also

References

  1. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ↑ Mineralienatlas
  3. 1 2 3 Handbook of Mineralogy
  4. 1 2 (Nordstrom and Alpers, 1999)
  5. 1 2 Mindat.org
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