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Sharp Dipyramidal Powellite

The Mineral powellite




Powellite is very similar to the mineral Scheelite, though it is much rarer. It forms a series with that mineral, and contains tungsten in place of the molybdenum. Powellite often forms as an alteration product of Molybdenite, sometimes only partially replacings it. Powellite is named after geologist John Wesley Powell (1834–1902), a director for the United States Geological Survey.
Chemical Formula CaMoO4
Composition Calcium molybdate, often with some tungsten
Variable Formula Ca(Mo,W)O4
Color White, beige, light yellow, light brown, orange, light blue, green
Streak White
Hardness 3.5 - 4
Crystal System Tetragonal
3D Crystal Atlas
(Click for animated model) 
Crystal Forms
and Aggregates
As small dipyramidal or pseudo-octahedral crystals, often with striations and sometimes with triangular growth layers. Also encrusting, grainy, and massive. May also form as an alteration product of Molybdenite assuming the original hexagonal or foliated shape.
Transparency Transparent to translucent
Specific Gravity 4.2
Luster Adamantine
Cleavage 3,1;2,1
Fracture Conchoidal to uneven
Tenacity Brittle
Other ID Marks Strong yellow fluorescence.
In Group Tungstates and Molybdates
Striking Features Crystal habits and fluorescence.
Environment In hydrothermal replacement deposits as a secondary mineral in molybdenum deposits, and in basalt traprock deposits and granite pegmatites.
Rock Type Igneous, Metamorphic
Popularity (1-4) 3
Prevalence (1-3) 3
Demand (1-3) 2


Powellite AUCTIONS



USES
Powellite is as a rare and expensive collectors mineral.

NOTEWORTHY LOCALITIES
Powellite is not a common mineral. It forms as a replacement mineral in molybdenum deposits, and its identity in these cases is frequently undetected (though it can easily be observed by its fluorescence). The largest single crystals, which are also of excellent form and highly aesthetic, come from the Indian traprock deposits of Nasik and Jalgaon, in Maharashtra state. A green, copper-rich Powellite comes from the Jardinera No. 1 Mine, in the Atacama Region of Chile. In the U.S., light green Powellite came from the Carlota Mine, Top of the World, Globe-Miami District, Gila Co., Arizona; and Molybdenite replacements from the Goodall Farm, Sanford, York County, Maine.

COMMON MINERAL ASSOCIATIONS
Quartz, Apophyllite, Molybdenite, Stilbite, Scolecite, Actinolite

DISTINGUISHING SIMILAR MINERALS
Scheelite - Fluoresces bright bluish-white, whereas Powellite fluoresces yellow.


powellite PHOTOS
 
ADDITIONAL RESOURCES
 
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