Monazite: Characteristics, Origin and Applications
One rich source of rare earth metals is monazite, a phosphate mineral crystal with chemical formula of (Ce, La)PO4. Monazite contains several rare earth metals, but in different concentrations: monazite-(Ce), for example, has a high cerium content. Other categories of monazite according to the major rare earth metal they contain include monazite-(La) which has high lanthanum content; monazite-(Nd) which has high neodymium content; and monazite-(Pr) which has high praseodymium content.
The most common color of monazite is reddish brown, although other samples excavated from known monazite deposits yielded monazite crystals that are colored brown, pale yellow, pink, grey, and even green. As a crystal, monazite is prismatic or wedge-shaped, with white streaks all around its surface. Monazite crystals range in appearance from translucent to opaque, with a luster that mineralogists describe as resinous, vitreous, or adamantine. Another major characteristic of monazite is its radioactivity. This is a result of monazite s thorium content, which can sometimes reach 20 to 30% of the mineral. It falls under 5.0 to 5.5 in the Mohs hardness scale.
Origin and History
Monazite was first discovered in the 1880s in a ship that carried monazite sand from Brazil. It was discovered by Carl Auer von Welsbach, who, during that time, has invented incandescent mantles that required a steady source of thorium in order to operate. Due to its radioactivity, interest in monazite grew especially in its potential as nuclear fuel. However, with the introduction of bastnasite (another rare earth metal-rich mineral) and the increased concern over the disposal of thorium s harmful radioactive by-products, monazite s popularity considerably fell.
This mineral s name was derived from a Greek word that translates into to be solitary a description that points to its isolated crystals. Brazil and India were the major sources of monazite before the World War. Other deposits are found in Madagascar and South Africa in Africa; Australia; Sri Lanka and Malaysia in Asia; and Norway, Austria, and Switzerland in Europe.
Uses and applications
Although the thorium content of monazite has limited its actual use in the years following the introduction of its alternative (bastnasite), monazite remains to have several uses and applications in industries and technology. It is a rich source of cerium, a rare earth metal used as a chemical oxidizing agent, polishing powder, and pigment for glass and ceramics, among other
things. It is also a source of lanthanum, a rare earth metal used in the manufacture of high refractive index glass, battery electrodes, camera lenses, and hydrogen storage.
Monazite also supplies industries with the rare earth metals neodymium and praseodymium. Neodymium is used in making rare earth magnets, lasers, ceramic capacitors, and violet pigment for glass and ceramics. Praseodymium, on the other hand, is used in the industries for the manufacture of rare earth magnets, lasers, core materials for carbon arc lighting, colorant in glasses and enamels, additive in didymium glass used in welding goggles, and the production of ferrocerium firesteel (flint) products.
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