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The Mineral uraninite

Cubic Uraninite Crystal

Uraninite is the most important radioactive mineral, and was once thought to be worthless. When the discovery of its useful uranium content was unveiled, it became extremely significant. It is the most common and widespread uranium mineral, making it the best known uranium ore. Many collectors refrain from collecting uranium minerals such as Uraninite because of their hazards and fragility. Uranium minerals should be kept out of light, preferably in a tight container, and unnecessary handling should be avoided. Hands should be washed after contact with any uranium mineral, and these minerals should not be stored in a room where one eats or sleeps on a regular basis.

Chemical Formula

UO2

Color

Greenish to brownish-black, steel-black, black

Crystal System

Isometric

Properties

Streak
Brownish-black, grayish-brown, olive-green
Hardness
5 - 6
Transparency
Opaque. Occasionally translucent in thin splinters.
Specific Gravity
6.4 - 10.6
Luster
Submetallic, greasy, pitchy, or dull
Cleavage
None
Fracture
Conchoidal to uneven
Tenacity
Brittle
Other ID Marks
Highly radioactive

Crystal Habits

Crystals are usually cubic, occasionally octahedral, and rarely dodecahedral. Crystals can also be a combination of these three types, especially cubes with octahedral corners.  Crystals are usually distorted and often have rounded edges. They may also have modified growth layers. Also occurs massive, botryoidal, earthy, grainy, as groups of small crystals, and as dendritic growths on rock.

3D Crystal Atlas

Additional Information

Composition
Uranium dioxide, sometimes with small amounts of thorium
In Group
Oxides; Simple Oxides
Striking Features
Radioactivity, high specific gravity, and crystal formations
Environment
In granite pegmatite veins and in hydrothermal replacement deposits.
Rock Type
Igneous, Metamorphic

Varieties

 -   Metamict, amorphous, impure variety of Uraninite. Pitchblende may be categorized by some as a separate mineral, but most references classify it as a variety of Uraninite.

Uses

Uraninite is the primary ore of uranium. Rare earth elements such as thorium and yttrium may also be mined from Uraninite.

Noteworthy Localities

Uraninite is found in many geographical areas, although mostly in small quantities. A classic European occurrence is Pribram, Bohemia, in the Czech Republic, which has produced fine botryoidal agglomerations. The occurrence of Katanga (Shaba), Congo (Zaire), has produced some of the finest and most lustrous crystals of Uraninite.

In the U.S., a very large deposit is in the Marysvale District, Piute Co., Utah, where Pitchblende occurs in enormous quantities. Excellent singe crystals have come from Topsham, Sagadahoc Co., Maine (especially the Swamp #1 Quarry), and dendritic Uraninite embedded in the host rock occurs in the Ruggles Mine, Grafton Co., New Hampshire, where it is often replaced by Gummite. Other well-known localities are Haddam and Portland, Middlesex Co., Connecticut and Spruce Pine, Mitchell Co., North Carolina.

In Canada, enormous crystals larger than any others were found at Wilberforce, Haliburton Co., Ontario, and good specimens have also come from Faraday Hill, Bancroft District, Hastings Co., Ontario.

Common Mineral Associations

Albite, Gummite, Uranophane, Zircon, Pyrite, Cassiterite, Chalcopyrite, Arsenopyrite, Quartz

Distingushing Similar Minerals

Magnetite - Attracted to magnets, not radioactive.
Spinel - Much lighter in weight, different streak.
Cassiterite - Different streak (white), not radioactive.
Columbite-Tantalite - Not radioactive, different crystal system.

uraninite Photos



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