monazite

Yellowish to reddish-brown color, vitre-ous to resinous luster, white streak.

Habit: crystalline, tabular, prismatic.
Color: black, gray, brown, red, yellow, green, or orange.
Diaphaneity: transparent to opaque.
Luster: adamantine, resinous (Th rich).
Streak: grayish white.
Cleavage: (001) distinct, (100) indistinct.
Twinning: {100} common.
Fracture: uneven, subconchoidal.
Chemical: slightly soluble in hot conc. H2SO4. When wetted by H2SO4, color the Bunsen flame in blue-green. Unfusible.
Deposits: granodiorites, syenites, granitic pegmatites, heavy mineral sands. 

Source of thorium, cerium, and other rare-earthmetals and compounds.

A natural phosphate of the rare-earthmetals, principally the cerium and lanthanide met-als, usually with some thorium. Yttrium, calcium,iron, and silica are frequently present. Monazitesand is the crude natural material and is usuallypurified from other minerals before entering com-merce.