Afwillite - Encyclopedia

    Class : Silicates
    Subclass : Nesosilicates
    Crystal System : Monoclinic
    Chemistry : Ca3(SiO3OH)2 2H2O
    Rarity : Very rare

Afwillite is a rare calcium silicate, formed during the contact metamorphism of limestones. Its name comes from the initials of the general manager of the DeBeers Consolidated Mines group : Alpheus Fuller Williams (1874-1953) after its discovery in the Dutoitspan diamond mine in Kimberley (South Africa). It occurs as colorless to white striated crystals, elongated prismatic or tabular, commonly grouped in fibroradiated spherolites, and in masses. Photo © Matteo Chinellato - Domenico Preite Collection

Afwillite in the World

The finest crystals come from the Northern Cape Province of South Africa, where the manganese mines in the Hotazel district yielded stunning 4.5 cm white prismatic crystals, and the Dutoitspan diamond mine near from Kimberley, rather badly formed crystals of 11 cm, the largest known, extracted from a block of dolerite reassembled by the kimberlite. Afwillite is also known in other sites, notably in Germany, near Brenk (Rhineland-Palatinate), in Italian Lazio such as Campomorto (main photo) or Viterbo.
6cm afwillite from Dutoitspan Mine, KEM JV Mine, Kimberley, South Africa - British Museum Collection - Photo © Rock Currier

Afwillite in France

In France, afwillite is present in the limestones of Boisséjour, near Clermont-Ferrand (Puy-de-Dôme).


No known twin for this mineral species.

Fakes and treatments

No known fakes or treatments.

Hardness : 3 to 4
Density : 2.63
Fracture : Conchoidal
Trace : White

TP : Translucent to transparent
RI : 1.617 to 1.634
Birefringence : 0.017
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None

Solubility : Hydrochloric and sulfuric acids

Magnetism : None
Radioactivity : None