Pseudomalachite

Pseudomalachite

Pseudomalachite from Flinders County, New South Wales, Australia. Specimen size 4.3 cm
General
Category Phosphate minerals
Formula
(repeating unit)		 Cu5(PO4)2(OH)4
Strunz classification 08.BD.05
Dana classification 41.04.03.01
Crystal system Monoclinic prismatic
Unit cell a = 4.47 Å, b = 5.75 Å, c = 17.05 Å; β = 91.06°; Z = 2
Identification
Formula mass 575.7 g
Color Dark emerald green to blackish green
Crystal habit Crystals, which are rare, are prismatic, usually with uneven faces. Pseudomalachite is commonly compact, reniform or botryoidal, or it may be fibrous or in crusts and films.
Crystal symmetry Monoclinic 2/m
Twinning On {100}
Cleavage Perfect on {100}, distinct on {010}
Fracture Splintery or conchoidal
Mohs scale hardness 4.5-5
Luster Vitreous
Streak Blue green, paler than the mineral
Diaphaneity Translucent to subtranslucent
Specific gravity (Measured) 4.15 to 4.35
Optical properties Biaxial (-)
Refractive index nα = 1.791 nβ = 1.856 nγ = 1.867
Birefringence δ = 0.076
Pleochroism Weak; X = bluish green to pale green; Y = yellowish green; Z = deep bluish green to blue-green
2V angle 48°
Dispersion Strong r<v. Also biaxial (+) r>v
Solubility Soluble in acids but without effervescence (in contrast to malachite which effervesces with warm HCl)
Other characteristics Not fluorescent, not radioactive
References [1][2][3][4]

Pseudomalachite is a phosphate of copper with hydroxyl, named from the Greek for “false” and “malachite”, because of its similarity in appearance to the carbonate mineral malachite, Cu2(CO3)(OH)2. Both are green coloured secondary minerals found in oxidised zones of copper deposits, often associated with each other. Pseudomalachite is polymorphous with reichenbachite and ludjibaite. It was discovered in 1813. Prior to 1950 it was thought that dihydrite, lunnite, ehlite, tagilite and prasin were separate mineral species, but Berry analysed specimens labelled with these names from several museums, and found that they were in fact pseudomalachite. The old names are no longer recognised by the IMA.[5]

Type Locality

The type locality is the Virneberg Mine, Rheinbreitbach, Westerwald, Rhineland-Palatinate, Germany. This is an area of ancient copper mining dating back to Roman times, and worked intermittently up until 1872.[1] The type material is held at the Mining Academy, Freiberg, Germany.[3]

Structure

The copper ions are co-ordinated by six oxygen ions to form distorted octahedra.[6] These octahedra are linked by sharing edges to form two distinct types of infinite chains, parallel to b. The chains are linked alternately, again by sharing octahedral edges, to form sheets parallel to the bc plane. Distorted phosphate tetrahedra link the sheets, and there is some doubt about the exact position of the hydrogen ions in the structure.[7]

Environment

It is a secondary mineral found in the oxidised zones of copper ore deposits. Associated with libethenite at several localities in New South Wales, Australia,[8] and at the Chino Mine, New Mexico, US.[9] Other associated minerals are apatite, azurite, chalcedony, chrysocolla, cornetite, cuprite, malachite, pyromorphite, tenorite, and iron oxyhydroxides.

Distribution

Pseudomalachite has been reported from Argentina, Australia, Austria, Belgium, Brazil, Canada, Chile, Czech Republic, Democratic Republic of Congo, France, Germany, Ireland, Israel, Italy, Japan, Kazakhstan, Madagascar, Mexico, Namibia, Norway, Poland, Portugal, Republic of Congo, Romania, Russia, Slovakia, South Africa, Spain, UK, US and Zambia.

References

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  1. 1 2 http://www.mindat.org/min-3299.html Mindat.org
  2. ↑ http://www.webmineral.com/data/Pseudomalachite.shtml
  3. 1 2 http://rruff.geo.arizona.edu/doclib/hom/pseudomalachite.pdf Handbook of Mineralogy
  4. ↑ Gaines et al (1997). Dana’s New Mineralogy Eighth Edition. Wiley
  5. ↑ Berry L G (1950). American Mineralogist 35: 365 to 385
  6. ↑ Ghose, Subrata (1963) The Crystal Structure of Pseudomalachite. Acta Crystallographica 16:124-128
  7. ↑ Shoemaker, G L, Anderson, J B and Kostiner, E (1977). American Mineralogist 62: 1042 to 1048
  8. ↑ The Australian Journal of Mineralogy 3:50, 10:55, 10:79, 11:97 and 11:117 to 118
  9. ↑ Rocks & Minerals (2009) 84:6 page 498
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