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Clarkeite

Big Photo

Bjertnes pegmatite, Krøderen Lake, Krødsherad, Buskerud, Norway
© Thomas Witzke

Show Clarkeite Photos (4)
Formula:
(Na,Ca,Pb)
 
2
U
 
2
(O,OH)
 
7
System:TrigonalColour:Dark red-brown, dark ...
Hardness:4 - 4½
Name:
After Frank Wigglesworth Clarke (1847-1931), American mineral chemist, and former Chief Chemist of the U.S. Geological Survey.


Clarkeite is a waxy to resinous dark brown replacement of uraninite. It is very uncommon, but is frequently misidentified with brown gummite that is dominated by schoepite group minerals. Frondel (1956) warmed: "Clarkeite is best identified by its X-ray powder pattern. It is indistinguishable from the dark brown types of oxidized uraninite ... and from dense brown types of fourmarierite and vandendriesscheite."

Classification of Clarkeite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:4/H.05-10
Nickel-Strunz 10th (pending) edition ID:4.GC.05

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
G : Uranyl Hydroxides
C : With additional cations; with mainly UO2(O,OH)6 hexagonal polyhedra
Dana 8th edition ID:5.4.1.1

5 : OXIDES CONTAINING URANIUM OR THORIUM
4 : AX2O7·xH2O
Hey's CIM Ref.:7.16.32

7 : Oxides and Hydroxides
16 : Oxides of U
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Type Occurrence of Clarkeite

Type Locality:Deer Park No. 2 Mine, Penland, Spruce Pine District, Mitchell Co., North Carolina, USA
Year of Discovery:1931

Physical Properties of Clarkeite

Lustre:Resinous, Waxy, Greasy
Diaphaneity (Transparency):Translucent
Colour:Dark red-brown, dark brown
Streak:Yellow-brown
Hardness (Mohs):4 - 4½
Fracture:Conchoidal, Sub-Conchoidal
Density (measured):6.39 g/cm3

Crystallography of Clarkeite

Crystal System:Trigonal
Cell Parameters:a = 3.954Å, c = 17.660Å
Ratio:a:c = 1 : 4.466
Unit Cell Volume:V 239.11 ų (Calculated from Unit Cell)
Z:3
Morphology:Massive, dense.
X-Ray Powder Diffraction:
d-spacingIntensity
5.903 (64)
3.365 (56)
3.195 (100)
2.945 (28)
2.707 (34)
1.977 (33)
1.8742 (19)
1.8554 (19)
1.6807 (14)
Comments:AM 82, p. 615; JCPDS 8-315 has extraneous and differing d-values.

Optical Data of Clarkeite

Type:Biaxial (-)
RI values: nα = 1.997 nβ = 2.098 nγ = 2.108
2V:Measured: 30° to 50°, Calculated: 32°
Birefringence:0.111
Maximum Birefringence:δ = 0.111

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:Very High
Dispersion:relatively weak

Chemical Properties of Clarkeite

Formula:
(Na,Ca,Pb)
 
2
U
 
2
(O,OH)
 
7
Essential elements:Na, O, U
All elements listed in formula:Ca, H, Na, O, Pb, U

Relationship of Clarkeite to other Species

Related Minerals - Nickel-Strunz Grouping):

- +
4.GC.10Umohoite
(UO
 
2
)MoO
 
4
·4H
 
2
O
4.GC.15Spriggite
Pb
 
3
[(UO
 
2
)
 
6
|O
 
8
|(OH)
 
2
]·3H
 
2
O
Related Minerals - Hey's Index Grouping:

- +
7.16.1Uraninite
UO
 
2
7.16.2Schoepite
(UO
 
2
)
 
8
O
 
2
(OH)
 
12
 · 12H
 
2
O
7.16.3Paraschoepite
UO
 
3
 · 2H
 
2
O
7.16.4Metaschoepite
UO
 
3
 · 1-2H
 
2
O
7.16.5Metastudtite
UO
 
4
 · 2H
 
2
O
7.16.6Studtite
[(UO
 
2
)(O
 
2
)(H
 
2
O)
 
2
]·H
 
2
O
7.16.7Ianthinite
U
4+
 
(UO
 
2
)
 
5
O
 
7
 · 10H
 
2
O
7.16.8Compreignacite
K
 
2
(UO
 
2
)
 
6
O
 
4
(OH)
 
6
 · 7H
 
2
O
7.16.9Vandenbrandeite
Cu(UO
 
2
)(OH)
 
4
7.16.10Roubaultite
Cu
 
2
(UO
 
2
)
 
3
(OH)
 
10
 · 5H
 
2
O
7.16.11Becquerelite
Ca(UO
 
2
)
 
6
O
 
4
(OH)
 
6
 · 8H
 
2
O
7.16.12Rameauite
K
 
2
Ca(UO
 
2
)
 
6
(OH)
 
16
 · H
 
2
O
7.16.13Agrinierite
K
 
2
(Ca,Sr)(UO
 
2
)
 
3
O
 
3
(OH)
 
2
 · 5H
 
2
O
7.16.14Protasite
Ba(UO
 
2
)
 
3
O
 
3
(OH)
 
2
 · 3H
 
2
O
7.16.15Billietite
Ba(UO
 
2
)
 
6
O
 
4
(OH)
 
6
 · 4-8H
 
2
O
7.16.16Bauranoite
Ba(UO
 
2
)
 
2
(OH)
 
6
 · 1-2H
 
2
O
7.16.17Metacalciouranoite
(Ca,Ba,Pb,K
 
2
)U
 
2
O
 
7
·2H
 
2
O
7.16.18Calciouranoite
(Ca,Ba,Pb)U
 
2
O
 
7
·5H
 
2
O
7.16.19Orthobrannerite
U
4+
 
U
6+
 
Ti
 
4
O
 
12
(OH)
 
2
7.16.20Thorutite
(Th,U,Ca)Ti
 
2
(O,OH)
 
6
7.16.21Davidite-(La)
(La,Ce)(Y,U,Fe)(Ti,Fe)
 
20
(O,OH)
 
38
7.16.22Davidite-(Ce)
(Ce,La)(Y,U,Fe)(Ti,Fe)
 
20
(O,OH)
 
38
7.16.23Brannerite
(U
4+
 
,Ca)(Ti,Fe
3+
 
)
 
2
O
 
6
7.16.24Fourmarierite
PbU
 
4
O
 
13
·4H
 
2
O
7.16.25Richetite
PbU
 
4
O
 
13
·4H
 
2
O
7.16.26Curite
Pb
 
3+x
(H
 
2
O)
 
2
[(UO
 
2
)
 
4
O
 
4+x
(OH)
 
3-x
]
 
2
7.16.27Masuyite
Pb(UO
 
2
)
 
3
O
 
3
(OH)
 
2
 · 3H
 
2
O
7.16.28Vandendriesscheite
PbU
 
7
O
 
22
·12H
 
2
O
7.16.29Metavandendriesscheite
PbU
 
7
O
 
22
·nH
 
2
O n < 12
7.16.30Sayrite
Pb
 
2
(UO
 
2
)
 
5
O
 
6
(OH)
 
2
·4H
 
2
O
7.16.31Wölsendorfite
(Pb,Ca)U
 
2
O
 
7
·2H
 
2
O
7.16.33Uranosphaerite
Bi(UO
 
2
)O
 
2
(OH)

Other Names for Clarkeite

Synonyms:
Brown Gummite
Other Languages:
German:Clarkeit
Russian:Кларкеит
Spanish:Clarkeita

Other Information

Fluorescence in UV light:none
Health Warning:radioactive

References for Clarkeite

Reference List:Ross, Henderson, and Posnjak (1931), American Mineralogist: 16: 213.

Palache, Charles, Harry Berman & Clifford Frondel (1944), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Volume I: Elements, Sulfides, Sulfosalts, Oxides. John Wiley and Sons, Inc., New York. 7th edition, revised and enlarged: 624-625.

Frondel, Clifford, 1956, Systematic Mineralogy of Uranium and Thorium, USGS Bulletin 1064, pp. 400.

Finch, Robert J. and Ewing, Rodney C., 1997, Clarkeite: New Chemical and Structural Data, American Mineralogist, 82: 607-619.

Finch, R.J. and R.C. Ewing (1997), Clarkeite: New chemical and structural data: American Mineralogist: 82: 607-619.

Kubatko, Karrie-Ann, Katheryn Helean, Alexandra Navrotsky, and Peter C. Burns (2006), Thermodynamics of uranyl minerals: Enthalpies of formation of uranyl oxide hydrates: American Mineralogist: 91: 658-666.

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    Localities for Clarkeite

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