Crude crystals of black Uraninite in Calcite from Bancroft, Ontario Canada
A crude Uraninite cubic crystal
from Bancroft, Ontario Canada
CHEMISTRY UO2 Uranium oxide
CRYSTALLOGRAPHY Isometric (Cubic)
CRYSTAL GROWTH AND HABITS Crystals of Uraninite are uncommon but are cubes modified by the octahedron and dodecahedron. It is also botryoidal, massive and may be dendritic.
COLOR AND OTHER OPTICAL PROPERTIES Uraninite is black and opaque.
HARDNESS 5 - 6
SPECIFIC GRAVITY 10.6 - 10.9 However, it rapidly decreases with oxidation to as low as 6.5.
LUSTER Submetallic to dull
STREAK Brownish black to gray or olive green
BREAKABILITY Uraninite has an uneven to conchoidal fracture and is brittle.
OCCURRENCE Uraninite is found in granite and in syenite pegmatites. It is also found in sulfide veins. Uraninite can also be found in sedimentary deposits as in the sandstones and conglomerates of the Colorado Plateau of the southwestern United States.
ASSOCIATED MINERALS Zircon, monazite, bismuth, barite, nickeline
OTHER PROPERTIES Uraninite is radioactive.
NAME derived from its composition