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Afwillite

• 
  Caspar quarry, Bellerberg volcano, Ettringen, Mayen, Eifel, Rhineland-Palatinate, Germany
  © Stephan Wolfsried

• Formula:
  Ca₃(HSiO₄)₂ · 2H₂O

• System: Monoclinic

• Name:
  Named after Alpheus Fuller Williams (1874-1953) of the Debeers Consolidated Mines.

• IMA Status: Valid (Grandfathered)

• Type Locality:
  Dutoitspan Mine, Kimberley, Northern Cape Province, South Africa

• Dana 8th: 52.4.7.1
  
  52 : NESOSILICATES Insular SiO₄ Groups and O,OH,F,H₂O
  4 : Insular SiO₄ Groups and O, OH, F, and H₂O with cations in [6] and/or >[6] coordination

• Hardness (Mohs): 3 - 4

• Density: 2.630 g/cm³ (measured)
  2.643 g/cm³ (calculated)

• Lustre: Vitreous

• Diapheny: Transparent

• Diapheny: brittle

• Colour: Colourless, white

• Streak: White