Mineral - Uraninite
Uraninite
Chemical Properties
Mineral Class
Oxides and Hydrxides
Toxicity
radioactive
Formula
UO₂
Unit Cell
a=5.47 Z=4
Physical Properties
Hardness
5 - 6
Streak
blackbrowngreen
Density
Very Heavy (>6)
Cleavage
Fracture
conchoidal,
uneven
Tenacity
Brittle
Optical Properties
Color
blackbrowngray
Birefringence
Luster
Greasy,
Metallic
Transparency
opaque
Pleochroism
Geomineralogical Properties
Crystal System
isometric
Point Group
hexoctahedral - 4/m 3 2/m
Space Group
Fm 3 m (225)
Habit
coarse, dodecahedron, massive, kidney-shaped, Octahedron, Cube
Formation
(1) Primarily magmatic, formed by fractional crystallization as an accessory mineral in granitic pegmatites and S-type granites.
(2) Hydrothermal, formed by precipitation in vein ore deposits.
(3) Sedimentary, formed by U precipitation under reducing, anoxic conditions (e.g. in sandstones)
(4) Due to its high mechanical and chemical resistance, found in alluvial placer deposits
Paragenesis
Twinning
Rarity
Rather rare
Synonyms
Uraninite
Composition
Elements
Mass
UO₃
22.69
ThO₂
0.20
CeO₂
0.71
UO₂
70.09
(Y,Er)₂O₃
3.41
La₂O₃
1.02
Al₂O₃
0.25
Fe₂O₃
0.10
PbO
0.40
CaO
0.30
H₂O
0.41
Mexico (Palache et al. 1952)
Groups and Members
Uraninite-Group