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Powellite

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Big Photo

Jardinera No. 1 Mine, Inca de Oro, Chañaral Province, Atacama Region, Chile
© Leon Hupperichs

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Formula:
Ca(MoO
 
4
)
System:TetragonalColour:Yellow, straw-yellow, ...
Lustre:Sub-Adamantine, Resinous, PearlyHardness:3½ - 4
Member of:Scheelite Group
Name:
Named after the American geologist and explorer, John Wesley Powell (1834-1902), second Director of the U.S. Geological Survey.
Isostructural with:Scheelite


Powellite-Scheelite Series.

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

Visit gemdat.org for gemological information about Powellite. Currently in public beta-test.

Classification of Powellite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:6/G.01-10
Nickel-Strunz 10th (pending) edition ID:7.GA.05

7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
G : Molybdates, Wolframates and Niobates
A : Without additional anions or H2O
Dana 7th edition ID:48.1.2.2
Dana 8th edition ID:48.1.2.2

48 : ANHYDROUS MOLYBDATES AND TUNGSTATES
1 : AXO4
Hey's CIM Ref.:27.3.2

27 : Sulphites, Chromates, Molybdates and Tungstates
3 : Molybdates
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Type Occurrence of Powellite

Type Locality:Peacock Mine (South Peacock; Darland; Peacock & South Peacock), Cuprum, Seven Devils District, Adams Co., Idaho, USA
Place of Conservation of Type Material:U.S. National Museum of Natural History, Washington, D.C., USA: #80674.
Year of Discovery:1891

Occurrences of Powellite

Geological Setting:Oxidation zone of hydrothermal deposits

Physical Properties of Powellite

Lustre:Sub-Adamantine, Resinous, Pearly
Diaphaneity (Transparency):Transparent, Translucent
Comment:Lustre sub-adamantine on crystal faces; greasy on fracture surfaces. Pearly lustre manifests on foliated pseudmorphous material.
Colour:Yellow, straw-yellow, yellow-brown, brown, greenish yellow, grey, blue or black, colourless; black material is deep blue in transmitted light.
Comment:May exhibit zoned colouration.
Hardness (Mohs):3½ - 4
Cleavage:Poor/Indistinct
Indistinct on {112} {011} and {001}.
Fracture:Irregular/Uneven
Density (measured):4.26 g/cm3
Density (calculated):4.255 g/cm3

Crystallography of Powellite

Crystal System:Tetragonal
Class (H-M):4/m - Dipyramidal
Space Group:I41/a
Cell Parameters:a = 5.222(1) Å, c = 11.425(3) Å
Ratio:a:c = 1 : 2.188
Unit Cell Volume:V 312.92 ų
Z:4
Morphology:Crystals dipyramidal {111}, with {011} and {112}; less commonly flat tabular to paper-thin on {001}, exhibiting many minor forms. Form e sometimes striated parallel to the intersection with vertical plane {110}; diagonal striations parallel to {131} observed on e and W. Tetragonal-dipyramidal symmetry evident only in the zones of [111]. Forms crusts; pulverulent; ocherous; massive.
Comment:On synthetic material
X-Ray Powder Diffraction:
Image Loading

Radiation - Copper Kα
Data Set:
Horizontal Axis: ° to ° Vertical Axis: % Source Data: Filtered Data:
Data courtesy of RRUFF project at University of Arizona, used with permission.

Optical Data of Powellite

Type:Uniaxial (+)
RI values: nω = 1.974 nε = 1.984
Maximum Birefringence:δ = 0.010

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:Very High
Pleochroism:Visible
Comments:In deeply colored specimens (Houghton County, Michigan, USA):
O = Blue
E = Green

Chemical Properties of Powellite

Formula:
Ca(MoO
 
4
)
Essential elements:Ca, Mo, O
All elements listed in formula:Ca, Mo, O
Analytical Data:
CaO (28.04%)
MoO3 (71.96%)
Empirical Formula:
CaMoO
 
4
Common Impurities:W

Relationship of Powellite to other Species

Series:Forms a series with Scheelite (see here)
Member of:Scheelite Group
Other Members of Group:

- +
Raspite
Pb(WO
 
4
)
Scheelite
Ca(WO
 
4
)
Stolzite
Pb(WO
 
4
)
Wulfenite
Pb(MoO
 
4
)
Common Associates:
StilbiteMolybdeniteMolybdeniteLaumontiteApophyllite
Related Minerals - Nickel-Strunz Grouping):

- +
7.GA.05Fergusonite-(Ce)
(Ce,La,Nd)NbO
 
4
7.GA.05Fergusonite-(Nd)
(Nd,Ce)(Nb,Ti)O
 
4
7.GA.05Fergusonite-(Y)
YNbO
 
4
7.GA.05Scheelite
Ca(WO
 
4
)
7.GA.05Stolzite
Pb(WO
 
4
)
7.GA.05Wulfenite
Pb(MoO
 
4
)
7.GA.10Formanite-(Y)
YTaO
 
4
7.GA.10Iwashiroite-(Y)
Y(Ta,Nb)O
 
4
7.GA.15Paraniite-(Y)
Ca
 
2
Y(AsO
 
4
)(WO
 
4
)
 
2
Related Minerals - Hey's Index Grouping:

- +
27.3.1Lindgrenite
Cu
 
3
(MoO
 
4
)
 
2
(OH)
 
2
27.3.3Wulfenite
Pb(MoO
 
4
)
27.3.4Koechlinite
Bi
 
2
MoO
 
6
27.3.5Sedovite
U(MoO
 
4
)
 
2
27.3.6Mourite
UMo
 
5
O
 
12
(OH)
 
10
27.3.7Iriginite
(UO
 
2
)Mo
 
2
O
 
7
 · 3H
 
2
O
27.3.8Umohoite
(UO
 
2
)MoO
 
4
 · 2H
 
2
O
27.3.9Moluranite
H
 
4
U
4+
 
(UO
 
2
)
 
3
(MoO
 
4
)
 
7
 · 18H
 
2
O
27.3.10Cousinite
MgU
 
2
Mo
 
2
O
 
11
 · 6H
 
2
O
27.3.11Calcurmolite
(Ca,Na)
 
2
(UO
 
2
)
 
3
Mo
 
2
(O,OH)
 
11
 · nH
 
2
O
27.3.12Tengchongite
CaO · 6UO
 
3
 · 2MoO
 
3
 · 12H
 
2
O
27.3.13Kamiokite
Fe
 
2
Mo
 
3
O
 
8
27.3.14Ferrimolybdite
Fe
 
2
(MoO
 
4
)
 
3
 · nH
 
2
O

Other Names for Powellite

Other Languages:
Catalan:Powellita
Dutch:Powelliet
German:Powellit
Italian:Powellite
Russian:Повеллит
Simplified Chinese:钼钙矿
钼酸钙矿
Spanish:Powellita

Other Information

Fluorescence in UV light:Creamy white or yellow to golden yellow (SW UV).
Other Information:May replace molybdenite leaving a material with a foliated structure appearance. Alters to Ferrimolybdite.

Decomposed by HCl and HNO3.
Health Warning:No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Powellite

Reference List:

- +
Melville (1891) American Journal of Science: 41: 138.

Koenig and Hubbard (1893) American Journal of Science: 46: 356.

Michel (1894) Bulletin de la Société française de Minéralogie: 17: 612.

Palache, C. (1899) American Journal of Science: 7: 367.

Pilipenko (1915) Bulletin of the Imperial Tomsk University, no. 63 [Min. Abs. (1923): 2: 109].

Larsen, E.S. (1921) The Microscopic Determination of the Nonopaque Minerals, First edition, USGS Bulletin 679: 122.

Zambonini (1923) Zeitschrift für Kristallographie, Mineralogie und Petrographie, Leipzig: 58: 248.

Vegard (1926) Philosophical Magazine and Journal of Science: 1: 1151.

Hintze, Carl (1889) Handbuch der Mineralogie. Berlin and Leipzig. 6 volumes: 1 [3B]: 4036.

Pough (1937) American Mineralogist: 22: 57.

Maucher (1938) Zs. Angew. Min.: 1 : 103.

Gianella (1941) University of Nevada Bull. 35, no. 6: 80.

Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II. John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged, 1124 pp.: 1079-1081.

National Bureau of Standards Circular 539 (1956), 6, 22.

Bulletin of the Mineralogical and Geological Society, Prague (1982): 27: 197-200.

Hazen, R.M., L.W. Finger, and J.W.E. Mariathasan (1985) High-pressure crystal chemistry of scheelite-type tungstates and molybdates. Journal of Physical Chemistry Solids, 46, 253–263.

Anthony, J.W., Bideaux, R.A., Bladh, K.W., and Nichols, M.C. (2003) Handbook of Mineralogy, Volume V. Borates, Carbonates, Sulfates. Mineral Data Publishing, Tucson, AZ, 813pp.: 563.

Internet Links for Powellite

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  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Powellite details from Handbook of Mineralogy (PDF)
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    • Localities for Powellite

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