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Cubic Uraninite Crystal
OXIDES; SIMPLE OXIDES · ISOMETRIC

Uraninite

UO2

Hardness
5–6
Streak
Brownish-black, grayish-brown, olive-green
Spec. Gravity
6.4–10.6
System
Isometric

About

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.

Crystal Forms & Aggregates

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.

Other ID Marks

Complex Tests

Striking Features

Environment

Varieties

✓ common  · ✗ uncommon

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

Distinguishing Similar Minerals

Photos

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Crystal forms

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Cube with Octahedral Modification
Cubic
Octahedral