Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Cubic
    Chemistry : ThO₂
    Rarity : Quite common

Thorianite is isostructural with uraninite with which there is an incomplete isomorphic series. Uranium-enriched terms are called uranothorianite, although the term uranium-bearing thorianite would be more accurate. Thorium is frequently substituted by rare earths, particularly by ceric rare earths (up to 8% Ce and La). Thorianite is highly radioactive, but never metamict because of the strong ionic bonds ensuring atomic cohesion. It is essentially a mineral of carbonate pegmatoids. Its name comes from the presence of thorium in its chemical composition. Thorianite is most often found in cubic crystals, sometimes twinned according to {111}, which can reach several centimeters of edge for a weight of 2 kg. The luster of thorianite is resinous to sub-metallic and its color is dark gray to black. Its high hardness (6.5 on the Mohs scale), its very high density (nearly 10), and its inalterability explain its good conservation in alluvium. For uranium terms, the oxidation of uranium leads to a lowering of the hardness. It is an ore of thorium and uranium.

Main photo : Thorianite from Betroka, Anosy, Madagascar © Rock Currier

Twinning on {111} are very common.

No fakes listed for this mineral species.