Remarkable New Silicate Structure

Abstract

Pabst, Gross and Alfors¹ described a new hydrated calcium silicate, named rosenhahnite after its discoverer. Lath-like single crystals up to 5 mm long were obtained and the morphology and physical characteristics measured. The composition of the crystals was found to be Ca₃Si₃O₉H₂O with two units in a triclinic unit cell. Thermal dehydration data showed that the molecule of water is given off very slowly at temperatures between 400 and 500° C and a single crystal of rosenhahnite transforms into an almost perfect single crystal of wollastonite, CaSiO₃, which is known to contain infinite Si₃O₉ chains. No visible cracking takes place and interfacial angles change little if at all, but the originally clear crystals become opaque and porcellaneous. From density measurements there is apparently about 5% of voids in the converted crystals, but these fissures are not large enough at the surface to admit toluene molecules. The perfect topotactic relation of the two lattices was established (apart from minor details) by the same investigators from partially transformed crystals, which gave almost equally sharp X-ray reflexions from both parts of the specimen.