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/cm³. 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