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Coffinite
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==Geological occurrence== Coffinite was first discovered in sedimentary uranium deposits in the Colorado Plateau region,<ref name=Min05/> but has also been discovered in sedimentary uranium deposits and hydrothermal veins in many other locations.<ref name=Hansley89/> Samples of coffinite from the Colorado Plateau were found with black fine-grained low-valence [[vanadium]] minerals, uraninite and finely dispersed black organic material.<ref name=":0" /><ref name=Stieff56/> Other materials associated with later finds from the same region were [[clay]] and [[quartz]].<ref name=Min05/> In vein deposits of the Copper King Mine in Colorado, coffinite was also found to occur with [[uraninite]] and [[pitchblende]].<ref name=Stieff56/> Coffinite is metastable<ref name=pnas15/> compared to [[uraninite]] and [[quartz]], thus formation of coffinite requires a [[uranium]] source in [[Redox|reducing conditions]], as evidenced by the associated presence of low-valence vanadium minerals.<ref name=Stieff56/> Silica-rich solution provides such a reducing condition in cases where coffinite results as an alteration product of [[uraninite]].<ref name=Zhang09/> Hansley and Fitzpatrick also noted that the brownish color of their coffinite samples was caused by organic material, leading them to conclude that coffinite can also form in low temperature conditions if organic carbon is present.<ref name=Hansley89/> This finding is consistent with the coffinite samples of the Colorado Plateau, which included fossilized wood.<ref name=Min05/> In China, coffinite can be found in [[granite]] in addition to [[sandstone]].<ref name=Min05/> Hansley and Fitzpatrick concluded that coarse-grained coffinite most likely forms in high temperature environments.<ref name=Hansley89/> Coffinite and uraninite precipitate inside brecciated and fractured regions of altered granite at pressures between 500 and 800 bars and temperatures at 126 to 178 Β°C.<ref name=Min05/>
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