Lavendulan

• The colour varies between turquoise and lavender, often also electric blue specimens can be found (see the picture below)
• Formula: NaCaCu₅(AsO₄)₄Cl · 5 H₂O
• Space group: P2₁/n (No. 14)
• Crystal system: monoclinic
• Crystal class: 2/m
• Lattice parameters: a =  10.011, b = 19.478 Å, c = 10.056 Å, α = 90° β = 90.37°, γ = 90°

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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).)

• CuO₅ and CuO₄Cl tetragonal pyramids (blue)
• CaO₇ polyhedra (light blue)
• NaO₆ distorted trigonal prismatic units (yellow)
• AsO₄ tetrahedra (green)
• Chlorine (bright green)
• Oxygen (red)
• Oxygen of water molecules (dark red)

For a 3D interactive version, see here:

https://skfb.ly/6qsoV

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