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, α = γ = 90°, β = 99.11°

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Picture: CC BY-SA 3.0 | Christian Rewitzer

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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

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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, α = β = 90°, γ = 120°

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Picture: CC BY-SA 3.0 | Christian Rewitzer

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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, α = β = 90°, γ = 120°

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Picture by Modris Baum (Public Domain)

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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