Chemistry of soil minerals. Part III. Synthetic micas with substitutions of NH4 for K, Ga for Al, and Ge for Si

Abstract

An investigation has been made of the hydrothermal synthesis of ammonium and potassium micas. The resultant ammonium aluminosilicate, gallosilicate, and gallogermanate micas have been compared with each other and with similarly prepared potassium aluminosilicate, gallosilicate, gallogermanate, and aluminogermanate micas. These micas have been characterised by their infrared spectra, by differential thermal and thermogravimetric analysis, and by X-ray diffraction. Unit cell dimensions and polytype character have been determined, and in the case of the potassium micas phases of compositions intermediate between those of the end-members have been prepared, and the relations between the dimensions of the unit cell and composition obtained.

The ammonium-bearing reaction mixtures yielded other crystalline compounds which included a new hexagonal aluminogermanate, an andalusite-type aluminogermanate, and, with lower ammonium hydroxide content, the clay minerals pyrophyllite and ammonium montmorillonite. The two aluminogermanates on ignition yielded the aluminogermanate analogue of mullite. Kaolin was found to recrystallise with ammonium hydroxide to ammonium mica, and alumina–germania–water gels in the absence of ammonium yielded boehmite and hexagonal germanium dioxide. β-Gallium oxide was an additional product in the synthesis of potassium gallosilicate micas.