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Formula: Ca1.3(V5+,V4+)6O16.6H2O
Vanadate,
hewettite group
Crystal System: Orthorhombic
Specific gravity: 2.77 to 2.79 measured 2.805 calculated
Hardness: 2½
Streak: Brownish green
Colour: Dark greenish black to black, turning brown on exposure to air
Environments
Sedimentary environments
Hydrothermal environments
Localities
There are two Co-Type Localities, the J J Mine, Paradox Valley, Uravan Mining District, Montrose County, Colorado, USA, and
the Nelson Point mine, Eastside mines, Shiprock District, San Juan County, New Mexico, USA.
Both of the mines are in vanadium-uranium
deposits in sandstone.
At the J J Mine, Paradox Valley, Uravan Mining District, Montrose County, Colorado, USA, the rear one-third of the mine
workings intersect the local water table and the water saturation has protected the ore from oxidation.
Below the water table, the ore is largely unoxidised and consists of vanadium
silicates, montroseite, uraninite and
coffinite. Disseminated pyrite and
marcasite are commonly associated with unoxidised ore.
Above the water table, in the middle part of the mine, remnants of relatively unoxidised rich ore associated with abundant
coalified plant material is surrounded by oxidised lower-grade ore that is disseminated in
sandstone.
Hendersonite is in partly oxidised ore that borders unoxidised ore, and it is associated with
paramontroseite, melanovanadite,
sherwoodite and corvusite. Close to the
portal of the mine the ore is mostly oxidised and consists chiefly of carnotite and
vanadium silicates.
Hendersonite forms in thin seams and veinlets in sandstone weakly
cemented by pyrite and marcasite. Small
amounts of goethite and
metatyuyamunite are also present
(AM 47.1252-1272).
At the Nelson Point mine, Eastside mines, Shiprock District, San Juan County, New Mexico, USA, the ore is at shallow depth
and is mostly oxidised. The chief ore minerals are vanadium silicates,
carnotite and tyuyamunite. Many bedding
planes in the ore zone contained films and seams of vanadium minerals, chiefly
hewettite and hendersonite. Gypsum
was present along many bedding planes in the vanadium-rich zone, as well as in
irregular fracture fillings.
Although most of the ore in the Eastside group of mines is oxidised because of its shallow depth, partly oxidised ore minerals
in addition to the hendersonite were found in several places. Greenish-black
corvusite occurs as a mineralised border between a
sandstone bed and a clay bed
(AM 47.1252-1272).
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