Chemistry of soil minerals. Part VII. Synthesis, properties, and crystal structures of salt-filled cancrinites

Abstract

Cancrinite has been synthesized in the sodalite crystallization field at 80° by addition of sodium nitrate, chromate, or molybdate. The crystals then contain these salts as guest species in place of the carbonate often found in natural cancrinites. This promotion of the formation of cancrinite was ascribed to association of anions with certain aluminosilicate species in solution, which then yielded cancrinite nuclei. As these grow into crystallites by addition of further anion–aluminosilicate complexes, the salt is incorporated into the 11-hedral cancrinite cages and into the wide channels enclosed by these. This behaviour was studied by investigations of conditions of synthesis and by chemical and thermal analyses, i.r. measurements, X-ray powder photography, and crystal-structure determinations based on powder data. The structure determinations were made for cancrinite nitrate (R= 0·12) and for a basic cancrinite containing some intercalated silicate (R= 0·07). The structures were compared with one recently determined for a natural cancrinite. In addition, partial refinement of two other cancrinites rich in sodium chromate and sodium molybdate served to locate these anions.