Hydrothermal Preparation of a Gehlenite Hydrate.

Hydrothermal treatment of synthetic gehlenite (2CaO.AlO.SiO) or of various mixtures of oxides, hydrates, etc., approximating the composition of gehlenite, at 260 to 650° C, produced a hitherto unreported compound having the composition 2CaO.AlO.SiO.HO. Other phases, usually hydrogarnet, were always present in small amounts. A natural gehlenite containing FeO and MgO was partly converted to the same hydrate at 450° C. The compound 2CaO.AlO.SiO.8HO was converted to a hydrogarnet at 250 °C, but formed 2CaO.AlO.SiO.HO at 350 °C. The new compound has a body-centered cubic structure, with a = 8.83 Å. The index of refraction is 1.628. An x-ray diffraction pattern is given, and some similarities between CaO.AlOSiO.HO and the ternary compound 4CaO.3AlO.3HO are pointed out.