Afwillite
- Named after the abbreviated discoverer Alpheus Fuller Williams (1874–1953), CEO of De Beers Consolidated Mines at that time
- Formula: Ca3(SiO3OH)2 · 2 H2O
- It belongs to the nesosilicates, i.e. there are only isolated SiO4 tetrahedra
- Space group: Cc (No. 9)
- Crystal system: monoclinic
- Crystal class: m
- Lattice parameters: a = 16.278 Å, b = 5.6321 Å, c = 13.236, α = γ = 90°, β = 134.898°
Picture: – http://www.mindat.org/photo-356015.html | CC BY-SA 3.0
Crystal structure (click on the pictures 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).)
- Oxygen (red)
- Hydrogen (white)
- SiO4 tetrahedra (yellow)
- CaO7 polyhedra (light blue)
For a 3D interactive version, see here:
The Fascination of Crystals and Symmetry 