Valentinite

• named in honour of Basilius Valentinus, a writer on alchemy. He is the supposed author of the first book to give a detailed description of antimony and its compounds.
• Formula: Sb₂O₃
• Space group: Pccn (No. 56)
• Crystal system: orthorhombic
• Crystal class: mmm
• Lattice parameters: a = 4.89960 Å, b = 12.4490 Å, c = 5.41030 Å, α = β = γ = 90°

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Picture: Christian Rewitzer | CC BY-SA-3.0

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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).)

• corner-connected SbO₃ pyramids (purple)
• Oxygen (red)

For a 3D interactive version on sketchfab, see here:

https://skfb.ly/6utNI

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Thaumasite – a suprising mineral

Thaumasite

• first described in 1878 in Sweden and named from the Greek, “thaumazein”, to be surprised, in reference to its unusual composition with carbonate, sulfate and hydroxysilicate anions
• Formula: Ca₃Si(OH)₆(CO₃)(SO₄)
• Space group: P6₃ (No. 173)
• Crystal system: hexagonal
• Crystal class: 6
• Lattice parameters: a = b = 11.0538 Å, c = 10.4111 Å, α = β = 90°, γ = 120°

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Picture: Rob Lavinsky| iRocks.com  | CC BY-SA-3.0

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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).)

• CaO₈ polyhedra (blue)
• SiO₆ octahedra (orange)
• SO₄ tetrahedra (yellow)
• CO₃ trigonalplanar coordination (gray)
• Oxygen (red)
• Hydrogen (white)

For a 3D interactive version on sketchfab, see here:

https://skfb.ly/6urWZ