Plancheite

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Plancheite

Plancheite and Malachite, Milpillas mine, Sonora, Mexico
General
Category Inosilicate
Formula
(repeating unit)		 Cu8Si8O22(OH)4•(H2O)
Strunz classification 09.DB.35
8/F.05-10
Dana classification 66.2.1.1
Identification
Formula mass 1171 g
Color Pale blue, light blue, dark green
Crystal habit Acicular, Fibrous, or Radial
Crystal system Orthorhombic mmm (2/m 2/m 2/m)
Cleavage None observed
Mohs scale hardness 5.5 to 6
Luster Vitreous to silky
Streak Light blue
Diaphaneity Translucent to opaque
Specific gravity 3.6 to 3.8
Optical properties Biaxial (+)
Refractive index

Nx = 1.645, Ny = 1.660 Nz = 1.715[1][2][3]

Nx = 1.697, Ny = 1.718, Nz = 1.741[4][5]
Pleochroism X colorless or pale blue, Y colorless or blue, Z blue or dark blue
Other characteristics Nonfluorescent, nonmagnetic, not radioactive
References [3][2][1][4]

Plancheite is a hydrated copper silicate mineral with the formula Cu8Si8O22(OH)4•(H2O). It is closely related to shattuckite in structure and appearance, and the two minerals are often confused.

Structure

Plancheite is a chain silicate (inosilicate), with double chains of silica tetrahedra parallel to the c crystal axis.[5] It occurs as sprays of acicular or fibrous radial clusters, with fibers extended parallel to the chains, i.e. along the c crystal axis;[4] it can also form tiny tabular or platy crystals. It is a member of the orthorhombic crystal class m m m (2/m 2/m 2/m), which is the most symmetrical class in the orthorhombic system.

Properties

Usually a pale turquoise-blue, with a pale blue streak and an adamantine to silky luster. It is quite hard, with hardness 5.5 to 6, close to that of feldspar, and specific gravity 3.6 to 3.8. Optically it is biaxial (+), with refractive indices between 1.64 and 1.74, and pleochroic.[1][2][3][4]

Environment

Plancheite is a secondary mineral formed in the oxidized zone of copper deposits, associated with other copper minerals chrysocolla, dioptase, malachite, conichalcite and tenorite.[4] It occurs with primary malachite at the Milpillas Mine in Mexico.[6] The type locality is the Sanda Mine, Mindouli, Pool Region, Republic of Congo.[1]

References

  1. ↑ 1.0 1.1 1.2 1.3 http://www.mindat.org/min-3233.html>
  2. ↑ 2.0 2.1 2.2 http://www.webmineral.com/data/Plancheite.shtml>
  3. ↑ 3.0 3.1 3.2 Gaines et al (1997) Dana's New Mineralaogy, Wiley>
  4. ↑ 4.0 4.1 4.2 4.3 4.4 http://www.handbookofmineralogy.org/pdfs/plancheite.pdf>
  5. ↑ 5.0 5.1 Evans and Mrose (1977) American Mineralogist 62:491-502
  6. ↑ Moore and Origlieri (2008) Mineralogical Record 39-6:25-34

External links

JMol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=00578

Plancheite, Kolwezi, Katanga (Shaba), Democratic Republic of Congo. 5.9 x 3.2 x 2.6 cm.
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