Uraninite is a mineral from the group of oxides, with the chemical formula UO2, it has a complex chemical composition and mineralogy due to being a radioactive mineral and prone to oxidation, it forms in granitic pegmatites and high-temperature hydrothermal veins, its use is widespread as primary uranium ore.
Physical properties and characteristics
| uraninite | Physical properties and characteristics |
|---|---|
| Class | Oxide |
| Brightness | Submetallic, greasy, matte. |
| Color | Black, grey. In some cases brown or greenish. |
| Stripe | black-brown |
| Chemical formula | UO2 (Uranium Dioxide) |
| Mohs hardness | 5.5 |
| Specific weight or density | 9-9.7 g/cm3 in gel varieties. 6.5-8.5g/cm3 |
| Cleavage or exfoliation | None |
| Fracture | Irregular, conchoidal to uneven |
| Tenacity | Fragile |
| crystalline system | Cubic |
| Way of introducing yourself (habit) | Usually botryoidal and massive, granular, columnar. Rarely in octahedron and dodecahedron, cubic crystals. |
| Origin or geological environment | They form in granitic and synthetic pegmatites, in high-temperature hydrothermal veins, and are found in sedimentary rocks. |
| associated rocks | Granitic pegmatites, sandstones, conglomerates, breccias. |
| Associated minerals | Albite, quartz, pyrite, arsenopyrite, cassiterite, zircon, pyrite, uranophane. |
| Applications | primary uranium ore |
It is the most important mineral that contains uranium and must be treated with care because it is highly radioactive. It has black hues, a sub-metallic, greasy or matte shine and a brownish-black streak.
It comprises a cubic crystalline system, in addition to a botryoidal, granular, columnar or massive habit, it has an irregular fracture and does not present cleavage.
Regarding its specific gravity, it is relatively high in unaltered samples, which can even have a specific gravity of 11. If the samples are affected by weathering or radioactive decay, the specific gravity can drop to 6.5.
Relation with gummite
It is a product of alteration of the uraninite, forms near the surface or in weathered surface deposits. The Gummite has a yellow color and is a mixture of uranium oxides, silicates and hydrates from oxidation and weathering.
For this reason, geologists are on the lookout for yellow, orange, and yellowish-green minerals near the surface that may indicate the presence of oxidized uraninite and gummite minerals.
Chemical composition
The uraninite It is a uranium dioxide (UO2). However, it presents an intermediate composition between UO2 and U3O8, this is due to the fact that most of the time the sample is oxidized and the uranium presents levels of radioactive decomposition, causing the mineral to have a complex chemical and mineralogical composition.
Most samples contain small amounts of materials such as argon, helium, cerium, lead, radium, yttrium, nitrogen, thorium, and more. Uranium can be replaced by thorium, forming thorianite ThO2.
Cleveite is an impure variety of the uraninite, in this material the first helium on Earth was discovered. Helium is an alpha decay product of uranium.
Origin, formation and geological environment.
It occurs as a primary mineral in granitic and synthetic pegmatites, where they exhibit octahedral, cubic, and modified shape habits. They have also been found as a precipitate in high temperature hydrothermal veins usually showing a botryoidal or granular habit.
This mineral is also found in sedimentary rocks such as heavy conglomerate debris, breccias, and coarse sandstones.
Small amounts of uraninites are sometimes found in sedimentary deposits associated with organic material.
Optical properties
Below is the uraninite in a thin section.
| Guy: | isotropic |
| Color in reflected light: | It is light gray with brown tint |
| Internal reflections: | Dark brown |
How to identify uraninite?
There are two useful properties to identify it in the field, which are the tendency to transform into yellow oxides and its radioactivity. A radiation detector can be used to look for them. Not all yellow materials may be a product of oxidation of the uraninite and the ones that are are usually radioactive.
Another important property is its high specific gravity, greater than 9 g/cm3 and less than 11 g/cm3, in addition to the fact that it has a hardness of 5.5 on the Mohs scale.
A test that was carried out is that, when concentrated nitric acid is placed in the sample, in the place where it was placed, it becomes fluorescent.
Uraninite Uses
- primary uranium ore
- In the extraction of elements such as thorium and yttrium.
Basically this mineral is the main ore of uranium, uranium is of great importance in the energy industry and also in the creation of nuclear weapons.
Interesting data
It is a dangerous and fragile mineral, it should not receive light and it is recommended that it be stored in an airtight container, you should also avoid handling it unnecessarily and wash your hands well after use and not keep it in the room where you eat or sleep.