Summary: Dickite from a new occurrence at Barkly East, Cape Province, is described and compared with a previously unreported dickite from Postmasburg and a dickite from Ouray, Colorado. The Barkly East dickite crystals are elongated in the direction of the a-axis; the ratio of length to width of crystals varies from 3:1 to 16:1. Optical, electron microscopic, X-ray, and thermal data and a chemical analysis are given. The thermogram of the fraction smaller than 2 µ e.s.d.1 is characterized by a single peak at 600°C., while that of fractions larger than 2 µ e.s.d. shows a double endothermal effect. This two-stage dehydroxylation of dickite on heating is attributed to a particle size effect.