DECOMPOSITION AND RESYNTHESIS OF THE MICAS*

A bstract A study was made of the ‐decomposition of the micas muscovite, phlogopite, biotite, and lepidolite and of the vermiculite Jefferisite. Decomposition was effected by heat, water vapor under pressure, and electrodialysis. The changes were generally detected by X‐ray methods supplemented by water‐loss determinations, differential thermal analysis, photomicrographs, and electron micrographs. Muscovite and phlogopite were found to have similar dehydration and decomposition characteristics, whereas biotite appeared to be more stable toward heat than either. Lepidolite, after a minor decomposition, may be melted and recrystallized congruently. Jefferisite decomposed to talc at about 350 °C. Low‐temperature arid low‐pressure hydrothermal experiments failed to produce any marked effects No intermediate products of decomposition were isolated in the high‐ temperature (maximum 650°C.), high‐pressure (maximum 10,000 Ib. per sq. in.) experiments. It was possible to resynthesize muscovite and phlogopite from their decomposition products. Electrodklysis was used for the first time as a tool for decomposing biotite and jefferisite in stages, finally reaching a silica gel. Other possible applications for electrodialysis were investigated.