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|System:||Trigonal||Colour:||Dark red-brown, dark ...|
|Hardness:||4 - 4½|
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) warned: "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:||18.104.22.168|
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|
|Colour:||Dark red-brown, dark brown|
|Hardness (Mohs):||4 - 4½|
|Density (measured):||6.39 g/cm3|
Crystallography of Clarkeite
|Cell Parameters:||a = 3.954Å, c = 17.660Å|
|Ratio:||a:c = 1 : 4.466|
|Unit Cell Volume:||V 239.11 Å³ (Calculated from Unit Cell)|
|X-Ray Powder Diffraction:|
|Comments:||AM 82, p. 615; JCPDS 8-315 has extraneous and differing d-values.|
Optical Data of Clarkeite
|RI values:||nα = 1.997 nβ = 2.098 nγ = 2.108|
|2V:||Measured: 30° to 50°, Calculated: 32°|
|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|
Chemical Properties of Clarkeite
|Simplified for copy/paste:||(Na,Ca,Pb)(UO2)O(OH)·0-1H2O|
|Essential elements:||H, 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):|
|Related Minerals - Hey's Index Grouping:|
Other Names for Clarkeite
|Fluorescence in UV light:||none|
References for Clarkeite
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.
Internet Links for Clarkeite
Localities for Clarkeite
The 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.
(TL) indicates type locality. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.
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