Epidote is being formed as a hydrothermal metamorphic product in metasediments in the Salton Sea geothermal system. One of the two analyzed epidotes has a composition of 32 mole percent Ca2Fe3Si3O12(OH) and occurs with chlorite, hematite, pyrite, quartz, albite, and K-feldspar. The second epidote has a composition of 20 mole percent Ca2Fe3Si3O12(OH) and occurs with iron-bearing tremolite, quartz, and pyrite. Both epidotes formed at temperatures of approximately 320°C and under 125-145 atm hydrostatic pressure. Variation in oxygen fugacity is the mechanism most likely to account for the different epidote compositions and mineral associations.

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