X-ray investigation of bredigite

Abstract

The X-ray work described below has been done on crystals of bredigite obtained from two different sources, the natural mineral from Scawt Hill, County Antrim, and the synthetic mineral from spiegeleisen slags. Both types of material have been fully deseribed by Tilley and Vincent (1948). Their analysis shows that the slag mineral is a calcium orthosilicate in which Ca is partly replaced by Mg, Mn, and Ba, the extent of the replacement being represented by the formula (Cal.59Ba0.08Mg0.31Mn0.09)SiO4. Tilley and Vincent conclude that this orthorhombic (pseudo-hexagonal) phase is identical with the high-temperature form α' of pure Ca2SiO4, the existence of which was suggested by Bredig (1943a), and confirmed by TrSmel (1949) using a high-temperature powder camera. Bredig (1943a) also suggests, on the basis of a comparison of X-ray powder patterns, that the crystal structure of α'-Ca2SiO4 is similar to that of β-K2SO4. The present single-crystal work was originally undertaken in order to investigate the structure of α'-Ca2SiO4 more fully.