Roger Weller, geology instructor
Powellite is a calcium molybdate mineral. Powellite crystallizes as transparent adamantine blue, greenish brown, yellow to grey typically anhedral forms. It exhibits distinct cleavage and has a brittle to conchoidal fracture. It has a Mohs hardness of 3.5 to 4. Powellite was first described in 1891 in the Peacock Mine, Adams County, Idaho and named for American explorer and geologist, John Wesley Powell (1834-1902).[i]
This example of willemite / calcite / powellite is from the Nellie James Mine in the Huachuca Mountains of Cochise County, AZ. Specimen is from the private collection of Roy Parsons.
Willemite is gray, Calcite is white, Powellite is white
Willemite is green, Calcite is red, Powellite is cream-white
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