Uranium in its natural compounds

The first minerals of uranium were described (specific appearance and properties) a long time before the element uranium was discovered. Their number, however, remained in a small limit after obtaining uranium oxide (Klaproth 1789) and the element uranium (Pekigot 1541). Only when the 2Oth century began the number of the known minerals of uranium, or of minerals with a fixed content of uranium, increased. According to the form of occurrence distinction can be made between primary and secondary minerals of uranium. They also differ with regard to their chemical valence (tetra- or hexavalent). In the description of the most important substitutes of both groups the essential attributes, the kind of occurrence, and the economic importance are mentioned. ( auth)