NEW MEMBERS OF THE HYDROTALCITE-MANASSEITE GROUP

Abstract

Several new minerals, structurally and chemically similar to the hydrotalcite-manasseite group, have been found in the saline deposits of the central pre-Caspian depression and in those of Middle Asia. Their structures consist of layers of (Mg//1// minus //xAl//x)(OH)//2 plus interlayers of anions and molecular water. In addition to manasseite itself, other varieties were identified whose interlayers contain alternately SO//4**2** minus or SO//4**2** minus and CO//3**2** minus anions. A unifying system of nomenclature is offered for consideration. In describing these brucite-like structures intercalated with anion- and cation-containing interlayers, the composition of the hydroxide sheet and the interlayers, the periodicity of the layers, and the mixed-layer nature of the material should be described. By means of symbols, a single term might be used to describe the crystal chemistry of any member of the group having a given cation composition for the brucite-like layers.