Afwillite is a calcium nesosilicate with formula Ca3(SiO3OH)2·2H2O. It occurs as glassy, colorless to white prismatic monoclinic crystals. Its Mohs scale hardness is between 3 and 4. It occurs as an alteration mineral in contact metamorphism of limestone It occurs in association with apophyllite , merwinite , ettringite , hillebrandite and calcite
It was first described in 1925 for an occurrence in the Dutoitspan Mine, Kimberley, South Africa and was named for Alpheus Fuller Williams (1874–1953), a past official of the De Beers diamond company.
Afwillite is typically found in veins of spurrite and it belongs to the nesosilicate sub-class. It is monoclinic, its space group is P2 and its point group is 2.