The mineral uraninite

	Chemical Formula	UO₂
	Composition	Uranium dioxide, sometimes with small amounts of thorium
	Variable Formula	(U,Th)O₂
	Color	Greenish to brownish-black, steel-black, black
	Streak	Brownish-black, grayish-brown, olive-green
	Hardness	5 - 6
	Crystal Forms and Aggregates	(Isometric) Crystals usually cubes, occasionally octahedrons, rarely dodecahedrons. Crystals are usually very distorted. Also occurs massive, botryoidal, earthy, grainy, as groups of small crystals, and as dendritic growths on rock.
	Transparency	Opaque. May or may not be translucent on 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
	Varieties	Pitchblende - Metamict, amorphous, impure variety of Uraninite. Pitchblende is occasionally categorized as a separate mineral. Cleveite - Uraninite containing up to 10 percent rare earth elements
	In Group	Oxides ; Simple Oxides
	All About	Uraninite 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. In general, most collectors do not collect uranium minerals, because of their hazards and fragility. Uranium minerals should be kept out of light, preferably in a sealed container, and should be handled as little as possible. Hands should be washed after contact with a uranium mineral.
	Uses	Uraninite is the primary ore of uranium. Rare earth elements are occasionally mined from Uraninite containing them.
	Striking Features	Radioactivity, high specific gravity, and crystal formations
	Complex Tests	If a drop of concentrated nitric acid is placed on Uraninite, that spot becomes strongly fluorescent.
	Popularity (1-4)	1
	Prevalence (1-3)	3
	Demand (1-3)	1
	Distinguishing Similar Minerals	Magnetite - attracted to magnets, not radioactive Black Spinel - much lighter in weight (3.5 - 4.1), different streak (white) Cassiterite - different streak (white), not radioactive Columbite-Tantalite - not radioactive, different crystal system (orthorhombic)
	Commonly Occurs With	Gummite, Uranophane, Torbernite, Autunite, Zircon, Pyrite, Feldspar, Cassiterite, Chalcopyrite, Arsenopyrite, Quartz
	Noteworthy Localities	Uraninite is found in most geographical areas, although mostly in small quantities. France, the Czech Republic, Germany, South Africa, and Canada are the largest producers of this important mineral. It occurs in Joachimsthal, Bohemia, Czech Republic; the Black Forest in Germany; Chameane, Puy-de-Dome, France; and in the Rossing Mine in South Africa. Occurrences of a lesser scale are Jaguaracu, Minas Gerais, Brazil; Carrara, Tuscany, Italy; Binntal, Wallis, Switzerland; Shinkolobwe mine, Shaba, Zaire; and numerous places in Cornwall, England. In the U.S., the largest deposit is in Marysvale, Utah, where Pitchblende occurs in enourmous quantities. Other localities are the Rock Landing Quarry in Middlesex Co., Connecticut; Central City, Gilpin Co., Colorado; and Spruce Pine, Mitchell Co., North Carolina. Dendritic Uraninite occurs in the Ruggles Mine, Grafton Co., New Hampshire, where it is often replaced by Gummite. The largest and most distinctive crystals in the U.S. come from the Swamp #1 Quarry, Topsham, Sagadahoc Co., Maine. In Canada, enormous crystals larger than any others were found at Wilberforce, Haliburton Co., Ontario.
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