   monazite is a reddish-brown phosphate mineral containing rare earth metals. it occurs usually in small isolated crystals. there are at least four different kinds of monazite, depending on relative elemental composition of the mineral:monazite group on mindat.org * 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 the elements in parentheses are listed in the order in which they are in relative proportion within the mineral: lanthanum is the most common rare earth element in monazite-(la), and so forth. silica, sio2, will be present in trace amounts, as well as small amounts of uranium and thorium. due to the alpha decay of thorium and uranium, monazite contains a significant amount of helium, which can be extracted by heating."helium from sand", march 1931, popular mechanics article bottom of page 460 monazite is an important ore for thorium, lanthanum, and cerium. it is often found in placer deposits. india, madagascar, and south africa have large deposits of monazite sands. 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 and, less commonly, uranium within monazite, it can be radioactive. because of its radioactive
Lanthanide_minerals Monoclinic_minerals Phosphate_minerals Thorium_minerals