Uranium

uranium

uraninite

autunite

torbernite

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: 1135^oC
Boiling point: 4130^oC
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)^-
Carbonates - the carbonate anion is (CO₃)^2-
Sulphates - the sulphate anion is (SO₄)^2-
Selenites - the selenite anion is (Se⁴⁺O₃)^2-
Tellurites - the tellurite anion is (Te⁴⁺O₃)^2-
Phosphates - the phosphate anion is (P⁵⁺O₄)^3-
Arsenates - the arsenate anion is (As⁵⁺O₄)^3-
Vanadates - the vanadate anion is (V⁵⁺O₄)^3-
Arsenite - the arsenite anion is (As³⁺O₃)^3-
Molybdates - the molybdate anion is (Mo⁶⁺O₄)^2-
Nesosilicates - insular (Si⁴⁺O₄)^4- groups
Organic Compounds

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