Anhydrous molybdate, scheelite group
Forms a series with scheelite
Specific gravity: 4.26
Hardness: 3½ to 4
Streak: Light yellow
Colour: Yellow, brown, greenish yellow, grey, blue or black, colourless; black material is deep blue in transmitted light.
Solubility: Decomposed by hydrochloric and nitric acid
Hydrothermal environments typical
Powellite is usually a secondary mineral, often
formed by the alteration of molybdenite. Also sometimes
formed in low-temperature hydrothermal environments, such as with
zeolites in vugs in
basalt or in some low-temperature
copper or mercury mines. More rarely formed in
contact metamorphic environments with
It is also occasionally found in granite
Powellite is associated with molybdenite, ferrimolybdite, stilbite, laumontite and apophyllite.
Near Nasik, Maharashtra, India, powellite occurs in vugs, grown partly on quartz and partly on laumontite, embedded in stilbite and apophyllite, and at Jalgaon it is associated with apophyllite.
At Bou Azzer, Morocco, powellite occurs is several locations. At Ightem it is found in dolomite boulders or resting on dolomite, conichalcite, malachite or olivenite. At Tandrost-West it is associated with annabergite and at Aghbar it occurs in quartz cavities with conichalcite.
At the South Hecla and Isle Royale mines, Houghton county, Michigan, USA, powellite is associated with native copper and epidote.
At the Tonopah Divide mine, Nye county, Nevada, USA, powellite occurs in vugs in altered rhyolite.
In the Nuratinsky range, Uzbekistan, powellite occurs in metasomatic deposits with scheelite and molybdenite.
Common impurities: W
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