A comparison of calcium sulfate dihydrate grown in clay gels and in sodium silicate gels

Abstract

A comparison of crystals of calcium sulfate dihydrate grown in two different gel media, sodium silicate gel and bentonite clay gel, shows that the two media affect crystal habit and surface topography differently. Those crystals grown in silica gel at 40°C and pH 7.5 consist of elongated prisms, exhibit relatively smooth crystal faces, and are often twinned. Crystals grown in bentonite gel at the same temperature and similar pH tend to be tabular, exhibit a wide variety of kinks, steps, and pits on their surfaces, and are never twinned under our experimental conditions. A comparison of the bentonite-grown crystals with those commonly found in nature shows that bentonite resembles natural sediments in its effects on growth habit of gypsum. © 1974.