monazite

A phosphate mineral containing rare-earth metals (lanthanides) such as lanthanum, cerium, yttrium, and thorium, and important as the major source of these metals. It occurs in granitic rocks and placer deposits.

In geology, the mineral monazite is a reddish-brown phosphate containing rare earth metals and an important source of thorium, lanthanum, and cerium. There are actually at least four different kinds of monazite, depending on relative elemental composition of the mineral:

monazite-Ce (Ce, La, Pr, Nd, Th, Y)PO4 monazite-La (La, Ce, Nd, Pr)PO4 monazite-Nd (Nd, La, Ce, Pr)PO4 monazite-Pr (Pr, Nd, Ce, La)PO2

The elements in parentheses are listed in the order in which they are in relative proportion within the mineral, so that lanthanum is the most common rare earth in monazite-La, and so forth.

Monazite is an important ore for thorium, lanthanum, and cerium.

Because of the presence of thorium within monazite, it can be radioactive.

The name monazite comes from the Greek mona`zein (to be solitary), in allusion to its isolated crystals.