UraniniteUO2
c 2001-2005 Mineral Data Publishing, version 1

Crystal Data: Cubic. Point Group: 4/m 3 2/m. Crystals uncommon, typically cubes
modified by the octahedron and dodecahedron, to 11 cm; botryoidal to reniform, colloform
banded, columnar, dense massive; may be dendritic. Twinning: On {111}, rare.
Physical Properties: Fracture: Uneven to conchoidal. Tenacity: Brittle. Hardness = 5–6
VHN = 499–548 (50 g load). D(meas.) = 10.63–10.95, decreasing markedly with oxidation, to as
low as 6.5. D(calc.) = 10.88 Radioactive.
Optical Properties: Opaque, transparent in thinnest fragments. Color: Steel-black tovelvet-black, brownish black, pale gray, pale green; in transmitted light, pale green, pale yellow,deep brown; pale gray with brownish tint in reflected light, may show dark brown internalreflections. Streak: Brownish black, gray, olive-green, shining. Luster: Submetallic to greasy,dull.
Optical Class: Isotropic.
R: (400) 17.6, (420) 17.3, (440) 17.0, (460) 16.8, (480) 16.5, (500) 16.3, (520) 16.2, (540) 16.0,(560) 15.9, (580) 15.8, (600) 15.9, (620) 15.9, (640) 16.0, (660) 16.0, (680) 16.1, (700) 16.2
Cell Data:

Space Group: F m3m (synthetic UO2.03 ).

a = 5.4682

Z=4X-ray Powder Pattern: Synthetic UO2.03 ; may be confused with thorianite or cerianite.
3.157 (100), 1.934 (49), 2.735 (48), 1.649 (47), 1.255 (18), 1.223 (15), 1.0523 (15)Chemistry:
UO3
ThO2
CeO2
UO2(Y, Er)2 O3
La2 O3Ce2 O3(1)
22.69
0.20
0.71
70.09
3.41
1.02(2)
20.1
14.3
50.0
0.0
0.1
0.8(1)
0.25
0.10

Al2 O3Fe2 O3FeOPbO
CaO
H2 O
rem.

0.40
0.30
[0.41]
0.12Total[99.70]

(2)

0.1
13.9
0.1

[99.4](1) Placer de Guadalupe, Chihuahua, Mexico; average of two analyses, H2 O calculated
from gain in weight on ignition. (2) Locality not stated; by electron microprobe; U4+ :U6+6+
from stoichiometry, original total given as 100.4%; corresponding to (U4+0.48 U0.18 Pb0.16 Th0.15
Ca0.01 Ce0.01 )Σ=0.99 O2.01 .
Mineral Group:

Forms a series with thorianite.

Occurrence: In granite and syenite pegmatites; in hydrothermal high-temperature tin andmoderate-temperature Co–Ni–Bi–Ag–As and other sulfide veins; in Colorado Plateau-type
sandstone-hosted U–V deposits; in uraniferous conglomerates; a detrital mineral.
Association: Zircon, monazite, tourmaline, mica, feldspar (pegmatitic); pyrite, chalcopyrite,galena, bismuth, silver, nickeline, barite, fluorite, carbonates (Co–Bi–Ag hydrothermal veins).
Distribution: Widespread; may form an important ore. At Jáchymov (Joachimsthal) and Hornı́
Slavkov (Schlaggenwald), Czech Republic. In Germany, from Johanngeorgenstadt, Schneeberg,and Annaberg, Saxony; in Bavaria, from Wölsendorf and Hagendorf. From many mines inCornwall, England. Large crystals from the Sierra Albarrana, Córdoba Province, Spain. At
Wilberforce, Ontario, and Great Bear Lake, Northwest Territories, Canada. In the USA, fromBranchville, Fairfield Co., Connecticut; Grafton, Grafton Co., New Hampshire; fine crystals
from Standpipe Hill, Topsham, Sagadahoc Co., Maine; around Spruce Pine, Mitchell Co., NorthCarolina; in the Ingersoll mine, near Keystone, Pennington Co., South Dakota. From Shinkolobwe
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and Kalongwe, Katanga Province, Congo (Shaba Province, Zaire). At Morogoro, Uruguru
Mountains, Tanzania.
Name:For URANium in the composition.

References: (1) Palache, C., H. Berman, and C. Frondel (1944) Dana’s system of mineralogy,(7th edition), v. I, 611–620. (2) Grandstaff, D.E. (1976) A kinetic study of the dissolution ofuraninite. Econ. Geol., 71, 1493–1506. (3) Janeczek, J. and R.C. Ewing (1992) Structural formulaof uraninite. J. Nuclear Materials, 190, 128–132. (4) (1953) NBS Circ. 539, 2, 33.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted inany form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior written
permission of Mineral Data Publishing.