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Powellite
Current inventory:  1 gem
 

Chemistry:  CaMoO₄   [Calcium Molybdenate]

Discovered in 1891;   IMA status: Valid (pre-IMA; Grandfathered).
Powellite is named after famed American explorer and geologist, John Wesley Powell (1834 - 1902). Lake Powell is also named after him.

Classification

Mineral Classification:

Molybdates and Wolframates

Strunz 8th Ed. ID:

6/G.01-10

Nickel-Strunz 10th Ed. ID: 

7.GA.05

7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
G : Molybdates, Wolframates and Niobates
A : Without additional anions or H₂O
05: Powellite - Scheelite series

Crystal Data

Crystallography:

Tetragonal - Dipyramidal

Crystal Habit:

Crystals are usually dipyramidal, less commonly flat tabular to paper-thin, with many minor forms, to 8 cm; may be aggregated into crusts, pulverulent, ocherous, massive.

Twinning:

None

Physical Properties

Cleavage:

[112] Indistinct, [011] Indistinct, [001] Indistinct

Fracture:

Uneven

Tenacity:

Brittle

Hardness (Mohs):

3.5 - 4.0

Density:

4.26 (g/cm³)

Luminescence:

Fluoresces creamy white or yellow to golden yellow under SW UV.

Radioactivity:

Not Radioactive

Optical Properties

Color:

Colorless, Straw Yellow, Greenish Yellow, Yellowish Brown, Brown; may be zoned, Blue to nearly Black

Transparency:

Transparent, Translucent

Luster:

Sub-Adamantine, Resinous, Pearly

Refractive Index:

1.974 - 1.984  Uniaxial ( + )

Birefringence:

0.011

Dispersion:

0.058 (higher than Diamond)

Pleochroism:

In deeply colored specimens; O = blue; E = green

Occurances

Geological Setting:

An uncommon secondary mineral, typically formed in the oxidation zone of molybdenum-bearing hydrothermal mineral deposits, rarely in basalts, tactites, and granite pegmatites.

Type Locality:

Peacock Mine, Cuprum, Seven Devils District, Adams County, Idaho, USA

Year Discovered:

1891

View mineral photos:

Powellite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Powellite is a rare member of the Scheelite group of minerals that also includes Scheelite, and Wulfenite. Powellite is an extremely rare gem, among the rarest of collector's gems. Prior to a discovery of Powellite crystals at Pandulena Hill, Nasik District, Maharashtra, India it was unknown as a gem. Gem quality crystals have since been found in the Jalgoan District of India as well. The transparent crystals from these locations are very small so gems are also small. There are several other locations worldwide where Powellite is found but none produce gem quality crystals.
 

  
Powellite gems for sale: