Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC-BY-SA-3.0], via Wikimedia Commons
An overview on Powellite Jewelry and Gems. Covers details and essential information on the physical properties and characteristics of Powellite gemstones.
| Data | Value |
|---|---|
| Name | Powellite |
| Crystallography | Tetragonal; crystals usually pyramidal (faces often striated), also tabular; massive, foliated, pulvurent, ocherous. |
| Refractive Index | 1.967-1.985 |
| 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 Luster | Greasy. |
| Hardness | 3.5-4 |
| Wearability | Poor |
| Fracture | Uneven |
| Specific Gravity | 4.23 (varies with tungsten content); Indian material 4.26 (colorless) to 4.28 (brown). |
| Birefringence | 0.011 |
| Cleavage | Indistinct |
| Dispersion | 0.058 |
| 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. |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, UV-Long, UV-Short |
| Transparency | Transparent to translucent. |
| Absorption Spectrum | Not diagnostic. |
| 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. Uniaxial (+). |
| Optic Sign | Uniaxial + |
Optics: o= 1.967-1.974; e = 1.978-1.985.
Uniaxial (+).
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; Russia; Morocco.
Name: After the American explorer and geologist, John Wesley Powell.
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