Uranyl ion, UO₂²⁺ is the most common ion for uranium compounds. This contains uranium in the +6 oxidation state and is by far the most stable of all uranium ions. Uranyl-units behave like metal ions and are not easily broken down. Many salts of uranyl are known, of which the nitrate is the most common one. The sample, shown here, is approximately 1 gram of the hexahydrate. The crystals are yellow/green fluorescent and have a somewhat glassy/transparent appearance.

A really spectacular display is obtained, when the solid is put in the light of a UV-A source, such as a common black-light TL tube. The picture below shows the same sample in a very dimly lit room, positioned approximately 7 cm from a black-light TL-tube. The compound shows a really bright brilliant green fluorescence.