Dioptase: emerald-green and visible cleavage planes

Dioptase

  • The name dioptase comes from the Greek words “dia” (= through) and “optos” (= visible), alluding to the visible cleavage planes inside the often highly transparent or translucent crystals
  • Formula: CuSiO3 · H2O
  • Space group: R-3 (No. 148)
  • Crystal system: trigonal
  • Crystal class: -3
  • Lattice parameters: a = b = 14.566 Å, c = 7.778 Å, αβ = 90°, γ = 120°

Dioptase Tsumeb

Dioptase Tsumeb

Picture: Didier Descouens – CC BY-SA 3.0


Crystal structure (click on the picture to download the VESTA file):

(K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,” J. Appl. Crystallogr., 44, 1272-1276 (2011).)

dioptase

View along the c axis.

  • six SiO4 tetrahedra (orange) are corner-connected to build a ring, so the mineral belongs to the cyclo silicates
  • the copper atoms (blue) are octahedrally coordinated by six oxygen atoms (red), four of them are oxygens involved in SiO4 tetrahedra and they occupy the equatorial positions of the CuO6 octahedra and two of them are oxygen atoms of water molecules, which occupy the axial positions of the CuO6 octahedra
  • the CuO6 octahedra are edge-connected and build a continuous 3D net
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