Electron probe measurements of natural zoned bravoite suggest complete solid solution of iron, cobalt, and nickel end members. Miscibility gaps indicated by experimental work were not found. It is concluded that natural bravoite is formed metastably from hydrothermal solutions at temperatures below those at which diffusion processes tend to decompose the metastable phase. The explanation is supported by thermodynamic reasoning and by experimental synthesis of zoned bravoite at temperatures below 300 degrees C.

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