Monazite

Monazite contains trace amounts of uranium and thorium, making it slightly radioactive. It's advisable to use a Geiger counter to measure radiation levels before handling. Wear gloves and a mask to prevent skin and lung exposure to radioactive dust. Wash your hands after handling it. Store it in a sealed container away from children and pets.

All monazites adopt the same structure, meaning that the connectivity of the atoms is very similar to other compounds of the type M(III)PO4. The M(III) centers have a distorted coordination sphere being surrounded by eight oxides with M–O distances around 2.6 Å in length. The phosphate anion is tetrahedral, as usual. The same structural motif is observed for lead chromate (PbCrO4).

Monazite is often mined as an ore for several rare elements and minerals. Thorium is one important component of this rock that can be used to generate nuclear power because it is very radioactive. Because monazite has these radioactive properties, it is often used for radioactive dating as well. It is also an important source of cerium and lanthanum.

Monazite sand from Brazil was first noticed in sand carried in ship's ballast by Carl Auer von Welsbach in the 1880s. Von Welsbach was looking for thorium for his newly invented incandescent mantles. Monazite sand was quickly adopted as the thorium source and became the foundation of the rare-earth industry. Monazite sand was also briefly mined in North Carolina, but, shortly thereafter, extensive deposits in southern India were found. Brazilian and Indian monazite dominated the industry before World War II, after which major mining activity transferred to South Africa. There are also large monazite deposits in Australia. Monazite was the only significant source of commercial lanthanides, but concern over the disposal of the radioactive daughter products of thorium, bastnäsite came to displace monazite in the production of lanthanides in the 1960s due to its much lower thorium content. Increased interest in thorium for nuclear energy may bring monazite back into commercial use.

The name monazite comes from the Greek μονάζειν (to be solitary), via German Monazit, in allusion to its isolated crystals.