Formula: Na4MgV5+10O28.24H2O
Decavanadate, pascoite group
Specific gravity: 2.39
Hardness: 2½ to 3
Streak: Yellow
Colour: Yellowish orange to orange
Solubility: Easily soluble in water
Melting point: 500oC

Sedimentary environments
Hydrothermal environments

Huemulite has been formed after opening copper-uranium deposits in sandstone and conglomerate; the vanadium may be derived from associated asphalt. Associated minerals include hummerite, rossite, thénardite, gypsum and epsomite (HOM).


At the type locality, the Huemul mine, Pampa Amarilla mining district, Malargüe Department, Mendoza Province, Argentina, the deposit is sedimentary. Basic volcanic bodies, predominantly hornblendiferous andesite, cut through the sediments, and there are some small outcrops of ignimbritic tuff. The uranium ore-bodies are located in conglomerate and sandstone, which is always associated with asphalt. It is suggested that the asphalt originates from the oil in the adjacent oil field of Pampa Amarilla. Uraninite is the principal uranium mineral, occurring with copper and iron sulfides such as chalcopyrite, chalcocite, covellite, bornite, idaite, pyrite, marcasite and small amounts of galena and sphalerite. No primary vanadium minerals have been found as yet. The probable source of the vanadium in huemulite is the asphalt. In the alteration zone above the water-table, many hydrated yellow minerals like tyuyamunite, sengierite, carnotite, cuprosklodowskite, autunite, bayleyite and andersonite are found in close association with copper minerals such as malachite, azurite and chalcanthite.
Huemulite was found the first time in the ore-body Agua Botada, and later in the Huemul and Agua Botada Sur mines. (AM 51.1-13). It occurs as fibrous crusts and films, as a post-mining product. Associated minerals include thénardite, rossite, quartz, hummerite, gypsum and epsomite (Mindat).

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