An overview on Powellite Jewelry and Gems. Covers details and essential information on the physical properties and characteristics of Powellite gemstones.
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|Crystallography||Tetragonal; crystals usually pyramidal (faces often striated), also tabular; massive, foliated, pulvurent, ocherous.|
|Colors||Straw yellow, greenish yellow. pale greenish blue, blue, blackish blue, dirty white (grayish) to gray, brown. blackish.|
|Luster||Subadamantine to greasy (on fracture surfaces).|
|Fracture||Uneven; brittle and fragile.|
|Specific Gravity||4.23 (varies with tungsten content); Indian material 4.26 (colorless) to 4.28 (brown).|
|Stone Sizes||The Michigan material is cuttable only to yield extremely minute stones, and until the Indian material was found powellite was essentially unknown as a gem material. The Indian crystals are quite transparent and cuttable, and gems up to about 3 carats have been cut. These are among the rarest of collector gems.|
|Luminescence||Fluoresces yellowish white-golden yellow in both LW and SW.|
|Formula||Ca(Mo,W)O4. Isostructural with Scheelite.|
|Pleochroism||Blue material is blue/green (Michigan); yellow material is yellow/light yellow (India).|
Optics: o= 1.967-1.974; e = 1.978-1.985.
Occurrence: A secondary mineral in the oxidation zone of ore deposits.
Houghton County, Michigan: blue cuttable material.
Utah; Nevada; California; Arizona; New Mexico.
Pandulena Hill, Nasik, India: unique occurrence, scattered crystals associated with zeolite minerals in basalt cavities.
Turkey; USSR; Morocco.
Name: After the American explorer and geologist, John Wesley Powell.