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The Mineral powellite

Sharp Dipyramidal 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

Color

White, beige, light yellow, light brown, orange, light blue, green

Crystal System

Tetragonal

Properties

Streak
White
Hardness
3.5 - 4
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.

Crystal Habits

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.

3D Crystal Atlas

Additional Information

Composition
Calcium molybdate, often with some tungsten
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

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

Distingushing Similar Minerals

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

powellite Photos



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