Afwillite, a new hydrous calcium silicate, from Dutoitspan mine, Kimberley, South Africa

Abstract

Mr. Alpheus F. Williams, General Manager of the De Beers Consolidated Mines, discovered in December, 1928, in the Dutoitspan mine, at Kimberley, crystals of a colourless mineral so different in appearance from other minerals observed in the Kimberley mines that it appeared to him to be new and worth detailed study. The mineral was found between the 500 and 750 ft. levels in a large dolerite inclusion in the kimberlite, and is associated with apophyllite, calcite, and natrolite. Up to the present time, less than a pound of the mineral has been found, and by far the larger part of this amount is represented by a few crystals of large size (11 × 4 × 1½ cm.). On closer examination, these crystals are seen to be not a single crystal, but a group of sub-parallel individuals, a type of development that is often observed on the larger crystals of many minerals.