Crystal Chemistry of Alkali Thorium Silicates Under Hydrothermal Conditions

An investigation into the crystal chemistry of the alkali thorium silicates resulted in the formation of five novel materials by hydrothermal synthesis. Of these, Rb4Th2Si12O30, and K2ThSi4O10F2 are new structure types crystallizing in space groups P1 and Pnma, respectively. The structure of Rb4Th2Si12O30 reveals a silicate sheet structure with eight-, six-, five-, and four-membered silicate rings. Crystals of a related composition, Cs2ThSi6O15, were also synthesized. They crystallize in space group Cmc21 and have a silicate sheet containing eight-, six-, and four-membered silicate rings. The structure of K2ThSi4O10F2 consists of a tubular silicate column comprised of eight-, six-, and four-membered silicate rings and features chains of fluorine-bridged Th atoms. Two new wadeite analogues Cs2ThSi3O9 and Rb2ThSi3O9 were also discovered and constitute the first actinide representatives in this mineral family. All products were crystallized from reactions of ThO2 and silica with alkali fluorides or hydroxid...