Symbol: U
Actinide (a chemical element with atomic number greater than 88), orthorhombic
Uranium does not occur naturally in the native state, but is found in several minerals such as
uraninite (pitchblende),
which is an important ore of uranium.
Specific gravity: 19.05
Hardness: 6.0 mohs
Colour: Silvery white
Solubility: Soluble in acids, but insoluble in alkalis
Melting point: 1135oC
Boiling point: 4130oC
Abundance in the Earth’s crust: 2.7 parts per million by mass, 0.25 parts
per million by moles
(ChC).
Abundance in the Solar System: 1 part per billion by mass, 4 parts per trillion by moles
(ChC).
72.75% of all vanadium deposits have uranium, and 13.23% of all
uranium deposits have vanadium
(Mindat).
Radioactivity: Uranium has no stable isotopes, so uranium-bearing minerals are invariably radioactive.
238U is the most stable isotope, with a half-life of 4.51 x 109 years (almost the age of the Earth)
(ChC).
Magnetism: Slightly paramagnetic
Oxidation states: When present in compounds, uranium exists mostly as U4+ and U6+
In primary rocks and magmas uranium is usually present in the quadrivalent state U4+. During early
crystallisation of the magma the low concentration of uranium prevents its crystallisation as distinct mineral
phases. The U4+, however, is large, and its size and charge keep it from becoming incorporated in the
usual rock-forming silicate minerals as they crystallise, and so the uranium tends to become concentrated in
the remaining hydrothermal solutions and pegmatites.
Ultimately the bulk of the uranium will crystallise as uraninite,
U4+O2, although in some hydrothermal vein deposits the primary uranium mineral is
coffinite U4+(SiO4).nH2O. Small amounts
may also be incorporated in accessory minerals such as zircon
Zr4+(SiO4),
monazite REE4+(SiO4)and
thorite Th4+(SiO4)
(Lauf2).
The uranyl ion is an oxycation of uranium in the oxidation state +6, with the chemical formula
(UO2)2+
Uranyl-bearing minerals include:
Hydroxides - the hydroxide anion is (OH)-
curite
kroupaite
masuyite
paulscherrerite
sayrite
shinkolobweite
spriggite
vandenbrandeite
Carbonates - the carbonate anion is (CO3)2-
albrechtschraufite
andersonite
astrocyanite-(Ce)
bayleyite
čejkaite
kamotoite-(Y)
lepersonnite-(Gd)
liebigite
rabbittite
schröckingerite
shabaite
sharpite
swartzite
voglite
Sulphates - the sulphate anion is (SO4)2-
ammoniozippeite
bobcookite
deliensite
feynmanite
gurzhiite
ježekite
johannite
libbyite
magnesiozippeite
marécottite
meitnerite
nickelzippeite
oldsite
pseudojohannite
rabejacite
redcanyonite
rietveldite
scenicite
seaborgite
shinarumpite
uranopilite
zincorietveldite
Selenites - the selenite anion is (Se4+O3)2-
demesmaekerite
derriksite
guilleminite
haynesite
marthozite
Tellurites - the tellurite anion is (Te4+O3)2-
cliffordite
moctezumite
schmitterite
Phosphates - the phosphate anion is (P5+O4)3-
autunite
bassetite
bergenite
chernikovite
coconinoite
furongite
kamitugaite
metanatroautunite
metatorbernite
metauranocircite
mundite
parsonsite
phosphowalpurgite
phosphuranylite
phuralumite
sabugalite
saléeite
torbernite
ulrichite
upalite
uranocircite
vochtenite
xiangjiangite
Arsenates
abernathyite
arsenuranylite
asselbornite
chistyakovaite
hallimondite
heinrichite
kahlerite
metanováčekite
metazeunerite
natrouranospinite
trögerite
uranospinite
walpurgite
zeunerite
Vanadates - the vanadate anion is (V5+O4)3-
ammoniomathesiusite
carnotite
francevillite
tyuyamunite
uvanite
Arsenites - the arsenite anion is (As3+O3)3-
seelite
Molybdates - the molybdate anion is (Mo6+O4)2-
umohoite
Nesosilicates - insular (Si4+O4)4- groups
boltwoodite
haiweeite
oursinite
parauranophane
sklodowskite
swamboite-(Nd)
uranophane
weeksite
Organic compounds
uroxite
Other uranium-bearing minerals, not necessarily uranyl minerals
davidite-(Ce)
davidite-(La)
elbrusite
uraninite
vapnikite
vorlanite
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