Some crystallographic studies in the system CaSO4–CaSOa4.2H2O II. The hydrous forms

Abstract

SummaryThe existence and relationships of hydrated forms both to one another and to anhydrous CaSO4 have been studied by X-ray methods. Detailed study of the hemi-hydrate reveals its true cell to be monoclinic and does not confirm the previously suggested polymorphism.Dehydration studies of the dihydrate and hemi-hydrate are reported; cyclic dehydration and hydration of single crystals of the latter show a variable temperature interval between the formation of γ-CaSO4 and the reconstitution of the hemihydrate at approximately constant humidity. An explanation of this behaviour is offered, and the structural implications of the results of the dehydration studies are discussed.