Some crystallographic studies in the system CaSOa4-CaSO4.2H2O I. The polymorphism of anhydrous CaSO4

Abstract

Summary: The existence and relationships of the polymorphs of CaSO₄have been studied by X-ray methods. Only two distinct phases are found: no crystallographic evidence is available to support the suggestion that theγ-CaSO₄structure can have two forms, and it is shown that most previous data on the existence of the high temperatureα-CaSO₄polymorphs are likely to be due to decomposition of the sulphate.Some observations on theγtoβ-CaSO₄transformation are reported. The structural implications of these results and their relevance to the nature of the transformation are discussed.