Monazite is a reddish-brown
phosphate mineral containing
rare earth metals. It occurs usually in small isolated
crystals. It has a hardness of 5.0 to 5.5 on the
Mohs scale of mineral hardness and is relatively
dense, about 4.6 to 5.7 g/cm
3. There are at least four different kinds of monazite, depending on relative elemental composition of the mineral:
- Monazite-(Ce), (Ce, La, Nd, Th)PO4 (the most common member)
- Monazite-(La), (La, Ce, Nd)PO4
- Monazite-(Nd), (Nd, La, Ce)PO4
- Monazite-(Sm), (Sm, Gd, Ce, Th)PO4