Coffinite stability

This approach leads to AG/(coffinite) = -449.9 kcal/mol. In good agreement, based on the high-tem-perature decomposition of coffinite to U02(c) and silica glass, Hemingway (1982) estimated AG (coffinite) = -450.76 kcal/mol, which is the value listed in Table A13.1. Because these estimates are based on the stability of U02(c), they probably refer to the stability of USi04(c). A more direct... 

Most natural uraninites or pitchblendes (and probably coffinites) are partially oxidized, with compositions between UO200 and UO267 (tl30g) (cf. Giblin 1987 Ahonen et al. 1993 Sunder et al. 1994). The stabilities of oxide phases of mixed oxidation state (between IV and VI) are shown in... 

The most recent development in sophisticated geochemical indicators of mineralization is Langmuir s saturation index (ST). The method yields a measure of the stability of uraniumbearing and associated minerals based on pH, Eh and major and trace elements in the groundwater. Positive SI values for uraninite or coffinite arc. . . strong indicators of the nearby presence of ore, as are positive SI values for the reduced phases of As, Mo, and Se. Regional trends in uraninite or coffinite SI values may exist, and should help locate possible ore zones even if no samples are close enough to the ore to show positive SI values for these phases. ... 

Coffinite is isostructural with zircon, thorite and hafnon and may show significant solid solution with each of these minerals. Its structure is shown in Fig. 3. No specific structural study has been done on coffinite. Crystals are always extremely small. The structure of the (OH)4 group may be implied by analogy with hydrogarnets. " Its role in the stability of coffinite is totally unknown. 

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