Monthly Archives: April 2017

Keyite – A Complex Copper-Zinc-Cadmium Arsenate

Keyite

  • Named after the mineral dealer Charley Key, who discovered some tiny blue crystals of this mineral on a sample of green Adamite
  • Formula: Cu3(Zn,Cd)4Cd2(AsO4)6· 2 H2O
  • Space group: I2/a (No. 15)
  • Crystal system: monoclinic
  • Crystal class: 2/m
  • Lattice parameters: a = 11.654 Å, b = 12.780 Å, c = 6.268 Å, αγ = 90°, β = 99.11°

Picture: CC BY-SA 3.0 | Christian Rewitzer


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).)

  • CuO4 square-planar units (blue)
  • CuO6 distorted octahedra (blue)
  • CdO6 distorted trigonal prismatic units (pink)
  • AsO4 distorted tetrahedra (green)
  • Oxygen (red)
  • Oxygen of water molecules (black(

For a 3D interactive version, see here:

https://skfb.ly/67tQD

Jarosite – Indicator of (liquid) water on Mars

Jarosite

  • Named after its type locality, Barranco del Jaroso in the Sierra Almagrera (near Los Lobos, Cuevas del Almanzora, Almería, Spain)
  • In 2004 the Mars Exploration Rover – B found Jarosite on Mars. Because on Earth Jarosite is only formed in liquid water, this finding strongly indicates that Mars once possessed large amounts of liquid water.
  • Formula: KFe3(OH)6(SO4)2
  • Space group: R-3m (No. 166)
  • Crystal system: trigonal
  • Crystal class: -3m
  • Lattice parameters: a = b = 7.304 Å, c = 17.268 Å, αβ = 90°, γ = 120°

Picture: CC BY-SA 3.0 | Christian Rewitzer


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).)

  • KO12 only very slightly distorted icosahedra (purple)
  • FeO6 octahedra (blue)
  • SO4 tetrahedra (yellow)
  • Oxygen (red)

For a 3D interactive version, see here:

https://skfb.ly/6pGuY

Ilmenite – the titanium dioxide source

Ilmenite

  • Named after it’s type locality, the Ilmensky Mountais in the Southern Urals (Russia)
  • Most important titanium mineral; it is predominantly mined for titanium dioxide production
  • Formula: FeTiO3
  • Space group: R-3 (No. 148)
  • Crystal system: trigonal
  • Crystal class: -3
  • Lattice parameters: a = b = 5.0884 Å, c = 14.0855 Å, αβ = 90°, γ = 120°

Picture by Modris Baum (Public Domain)


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).)

  • FeO6 distorted octahedra (brown)
  • TiO6 distorted octahedra (blue)
  • Oxygen (red)
  • The structure can be derived from the corundum (Al2O3) type: in corundum all cations are identical but in ilmenite Fe2+ and Ti4+ ions occupy alternating layers perpendicular to the c axis
  • Within the alternating layers the FeO6 / TiO6 octahedra are edge-connected to give six-membered rings (the centre of the hexagons are unoccupied)

For a 3D interactive version, see here:

https://skfb.ly/6ps9E