Radioactive ore, source of thorium, terbium, and cerium
Monazite is a reddish-brown phosphate mineral containing rare earth metals and is an important source of thorium, terbium, and cerium. It occurs usually in small isolated crystals.
Monazite is an important ore for thorium, terbium, and cerium. It is often found in placer deposits. The deposits in India are particularly rich in monazite. It has a hardness of 5.0 to 5.5 and is relatively dense, about 4.6 to 5.7 g/cm3.
Because of the presence of thorium within monazite, it can be radioactive. If samples are kept, they should be placed away from minerals that can be damaged by radiation. Because of its radioactive nature, the monazite within rocks is a useful tool for dating geological events, such as heating or deformation of the rock.
The name monazite comes from the Greek µ??a?e?? (to be solitary), in allusion to its isolated crystals.