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Uranium is a silver-white, lustrous, heavy, mildly radioactive metal. Its appearance will change upon exposure to air or water, as oxidation occurs. Its colour darkens through brass, from brown to charcoal grey. Powders, fines, chips, or turnings oxidise rapidly, yielding a dull or flat dark grey or brown colour. Uranium is almost as hard as steel and much denser than lead. Natural uranium is used to make fuel for nuclear power plants; depleted uranium is the leftover product. Some alloys will oxidise more slowly, retaining the silver-white and then brassy colour. No odour is found. Uranium is used as an abundant source of concentrated energy. Uranium occurs in most rocks in concentrations of 2–4 parts per million and is as common in the Earth’s crust as tin, tungsten, and molybdenum. Uranium occurs in seawater and can be recovered from the oceans.
Uranium is a naturally occurring radioactive element. Natural uranium is a mixture of three isotopes: 234U, 235U, and 238U. The most common isotope is 238U; it makes up about 99% of natural uranium by mass. Depleted uranium is a mixture of the same three uranium isotopes except that it has very little 234U and 235U. It is less radioactive than natural uranium. The high density of uranium means that it also finds uses in the keels of yachts and as counterweights for aircraft control surfaces, as well as for radiation shielding. Uranium metal is known to react dangerously with carbon tetrachloride, chlorine, fluorine, nitric acid, nitric oxide, selenium, sulphur, and water (in finely divided form). On decomposition with fire, it produces uranium metal fume and/or oxide. Radioactive progenies (daughters), thorium-234, protactinium-234, and protactinium-234m (metastable), are produced by natural radioactive decay; they are the source of the majority of the penetrating radiation. These isotopes can be concentrated in situations where the metal is melted, condensed, or dissolved, potentially elevating the observed external dose rate. Many industries involved in mining, milling, and processing of uranium can also release it into the environment. Inactive uranium industries may continue to release uranium into the environment.

Uranium is a white radioactive metallic element found in pitchblende ore, also known as uraninite. Uranyl chloride and uranyl nitrate are two uranium compounds used in photography.

A highly toxic element on an acute basis. The permissible levels for soluble compounds are based on chemical toxicity, whereas the permissible body level for insoluble compounds is based on radiotoxicity. The high chemical toxicity of uranium and its salts is largely shown in kidney damage, which may not be reversible. Acute arterial lesions may occur after acute exposures. The most soluble uranium compounds are UF6, UO2(NO3)2, U02Cl2, UO2F2, and uranyl acetates, sulfates, and carbonates. Some moderately soluble compounds are UF4, UO2, UO4, (NH4)2 U2O7, UO3, and uranyl nitrates. The rapid passage of soluble uranium compounds through the body tends to allow relatively large amounts to be absorbed. Soluble uranium compounds may be absorbed through the skin. The least soluble compounds are high-F2ed UO2, U3O8, and uranium hydrides and carbides. The high toxicity effect of insoluble compounds is largely due to lung irradation by inhaled particles. This material is transferred from the lungs of animals quite slowly. A very dangerous fire hazard in the form of a solid or dust when exposed to heat or flame. It can react violently with air, Cl2, F2, HNO3, NOx Se, S, water, NH3, BrF3, trichloroethylene, nitryl fluoride. During storage it may form a pyrophoric surface due to effects of air and moisture. Depleted uranium (the 238U by-product of the uranium enrichment process, with relatively low radioactivity) is used in armor-piercing shells, ship or aircraft ballast, and counterbalances. Uranium is also used in making colored ceramic glazes.

Three isotopes (234U, 235U, 238U) exist, and a large number of uranium salts are known. They present both toxic and radiological hazards. The most important use of uranium is in the nuclear energy industry, but uranium compounds are also used in ceramics, as catalysts and in certain alloys. Entry into the body can occur during a variety of processes involved with the mining, processing or use of uranium and its compounds, and is probably largely by inhalation of dusts, fumes, etc. or by ingestion. Acute uranium toxicity is primarily nephrotoxicity. About 50% of plasma uranium is bound, as the uranyl ion, to bicarbonate (HCO23 ), which is filtered by the glomerulus. As a result of acidification in the proximal tubule, the bicarbonate complex dissociates followed by reabsorption of the HCO23 ; the released UO21 then becomes attached to the membrane of the proximal tubule cells. Loss of cell function follows, as evidenced by increased concentration of glucose, amino acids, and proteins in the urine. 2,3-Mercapto-1-propanol (British Anti-Lewisite, BAL) is ineffective as a therapeutic agent for uranium poisoning; CaEDTA is recommended. Chronic uranium toxicity appears to be radiation related, the effects being similar to those of ionizing radiation. In humans, cancer of the lung, bone, and lymphatic system are all known to occur.