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Named for the chemical constituents of ferric iron (ferri), which is iron with the oxidation number 3+, and molybdenum (molybd). Somewhat uncommon but widespread, Ferrimolybdite can be found in small amounts and as well studied material in localities in Russia, Belgium, the United States, Australia, and China, as well as numerous other, less well studied localities. It occurs in oxidized molybdenum-bearing hydrothermal vein and porphyry deposits as a secondary mineral.
Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/ferrimolybdite.pdf