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Powellite

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John Wesley Powell, second Director of the USGS. Served from 1881-1894. Profile early in his term of office as Director
Formula:
Ca(MoO4)
System:
Tetragonal
Colour:
Yellow, straw-yellow, ...
Lustre:
Sub-Adamantine, Resinous, Pearly
Hardness:
3½ - 4
Member of:
Name:
Named in 1891 by William Harlow Melville in honor of the American geologist and explorer, John Wesley Powell [March 24, 1834 Mount Morris, New York. USA – September 23, 1902 North haven, Maine, USA], second Director of the U.S. Geological Survey.
Isostructural with:
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.


Classification of Powellite

Approved, 'Grandfathered' (first described prior to 1959)
7.GA.05

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

48 : ANHYDROUS MOLYBDATES AND TUNGSTATES
1 : AXO4
27.3.2

27 : Sulphites, Chromates, Molybdates and Tungstates
3 : Molybdates

Occurrences of Powellite

Type Occurrence of Powellite

Place of Conservation of Type Material:
U.S. National Museum of Natural History, Washington, D.C., USA: #80674.

Physical Properties of Powellite

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:
4.26 g/cm3 (Measured)    4.255 g/cm3 (Calculated)

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:
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
Max Birefringence:
δ = 0.010
Image 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(MoO4)
All elements listed in formula:
Analytical Data:
CaO (28.04%)
MoO3 (71.96%)
Empirical Formula:
CaMoO4
Common Impurities:
W

Relationship of Powellite to other Species

Series:
Forms a series with Scheelite (see here)
Member of:
Other Members of Group:
RaspitePb(WO4)
ScheeliteCa(WO4)
StolzitePb(WO4)
WulfenitePb(MoO4)
7.GA.05Fergusonite-(Ce)(Ce,La,Nd)NbO4
7.GA.05Fergusonite-(Nd)(Nd,Ce)(Nb,Ti)O4
7.GA.05Fergusonite-(Y)YNbO4
7.GA.05ScheeliteCa(WO4)
7.GA.05StolzitePb(WO4)
7.GA.05WulfenitePb(MoO4)
7.GA.10Formanite-(Y)YTaO4
7.GA.10Iwashiroite-(Y)Y(Ta,Nb)O4
7.GA.15Paraniite-(Y)Ca2Y(AsO4)(WO4)2
27.3.1LindgreniteCu3(MoO4)2(OH)2
27.3.3WulfenitePb(MoO4)
27.3.4KoechliniteBi2MoO6
27.3.5SedoviteU(MoO4)2
27.3.6MouriteUMo5O12(OH)10
27.3.7Iriginite(UO2)Mo2O7 · 3H2O
27.3.8Umohoite(UO2)MoO4 · 2H2O
27.3.9MoluraniteH4U4+(UO2)3(MoO4)7 · 18H2O
27.3.10CousiniteMgU2Mo2O11 · 6H2O
27.3.11Calcurmolite(Ca,Na)2(UO2)3Mo2(O,OH)11 · nH2O
27.3.12TengchongiteCaO · 6UO3 · 2MoO3 · 12H2O
27.3.13KamiokiteFe2Mo3O8
27.3.14FerrimolybditeFe2(MoO4)3 · nH2O

Other Names for Powellite

Name in Other Languages:
Catalan:Powellita
Dutch:Powelliet
German:Powellit
Italian:Powellite
Spanish:Powellita

Other Information

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 Risks:
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

mindat.org URL:
http://www.mindat.org/min-3275.html
Please feel free to link to this page.
Specimens:
The following Powellite specimens are currently listed for sale on minfind.com.

Localities for Powellite

map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
Mineral and/or Locality  
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