It has only been within the past few years that monazite has become one of the important economic mineral products, in its use for the manufacture of the incandescent mantles of the Welsbach light) Previous tO that time it was considered one of the rare minerals, as denoted by its name, a derivation~ from the Greek, meaning "to be solitary."
The demand created by the manufacturers of the incandescent gas lights for the rare earth minerals stimulated the search for monazite, and it was soon found to exist in certain deposits and rocks, where its presence had not before been suspected, and so necessity became the mother of discovery.
Monazite is essentially a phosphate of the rare earths, cerium, lanthanum and didymium (Ce. La. Di.) PO4. It also contains, almost always, small variable percentages of thoria (ThO2) and silica (SiO,~), which by some are supposed to be present in combination, as an impurity, in the form of thorite or orangite (Th.SiO4.H20), while others believe that the thoria is a primary constituent, present originally as the phosphate, either in combination with cerium or as an isomorphous compound, and afterwards altered to the silicate by siliceous waters.