Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Cubic
    Chemistry : UO₂
    Rarity : Common

Uraninite is the natural oxide of uranium, but some confusion remains between the terms "uraninite" and "pitchblende". The international mineralogical nomenclature recommends the term uraninite to designate the natural oxide of tetravalent uranium in all its facies. However, according to Dana (1861), the term uraninite is still too often reserved in the literature for facies with clear crystalline forms, the term pitchblende designating in contrast the collomorphic facies of uranium oxide. Its name comes from its chemical composition. Uraninite is much more common in its collomorphic facies (pitchblende), and then constitutes aggregates of spherulites whose dimensions can exceed 20 cm in diameter, forming hummocky masses. While automorphic uraninite is predominantly magmatic, pitchblende is a facies of uraninite of hydrothermal origin, common in many veins and in detrital sedimentary rocks. Whatever its facies, uraninite is black in color and has a submetallic to resinous luster as well as a conchoidal fracture. It is characterized by a high density (variable according to the oxidation state of uranium : from 7.5 to more than 10), and obviously by a very high radioactivity. From a chemical point of view, the structural relationship of uraninite with thorianite explains the existence of a solid solution between these two minerals. It has been proven that this was artificially continuous. Highly alterable at outcrops, uraninite epigenizes or transforms into an impressive procession of powdery minerals of yellow to orange hue, rarely black, collectively designated under the name of "gummites". It is the main ore of uranium.

Main photo : Uraninite from Shinkolobwe Mine, D.R. Congo © Eugene & Sharon Cisneros

Twinning is known on {111}.

No fakes listed for this mineral species.