MONAZITE MINERAL FACTS Nevada Turquoise gem stones
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Monazite Mineral Facts:

Chemical Formula: (Ce,La,Pr,Nd,Th,Y)PO4
A phosphate of cerium and the other rare earth metals. Monazite has been identified in Cerium, Lanthanium, Neodymium and Praseodymium rich versions. Cerium dominates in nearly all monazite deposits. It also normally contains some Thorium and Uranium, as well as some silica.

Colors: Yellowish to reddish brown or green.

Hardness: 5 to 5.5  
Hardness is such that the material easily writes on paper and soils fingers handling the specimen, giving a greasy feel to the touch.

Density: 5.2 to 5.3

Cleavage: One distinct cleavage on 100

Crystallography: Monoclinic
Individual crystals are rare, but do occur in pegmatites. Typically small, often flattened parallel to the orthopinacoid. Normally found in granular masses, frequently as sand.

Luster:. Resinous luster. Translucent to opaque.

Optics: (Refractive Index): a=1.7038, y=1.8452

Monazite - Crystal form, Pakistan

Monazite - Crystal form, Pakistan

 


Composition, Structure and Associated Minerals:
Monazite is a
comparatively rare mineral occurring as a minor accessory mineral in the form of small grains and crystals scattered through certain granites, granitic schists and pegmatites. It is found in pegmatite veins at many localities, associated with quartz and felspar. In these veins it usually occurs as fairly large crystals and fragments of a brownish color. In these primary forms it is a separation on cooling from the granitic magma. It is found only in very small percentages in these rocks. However because it is dense and resists weathering, when the granites are broken down into sand by weathering the monazite is freed and concentrated into commercial quantities in alluvial stream channels and sand deposits. Most commercial deposits are found in layered beach sands.

Identification and Diagnostics
The mineral is infusible. Before the blow pipe it turns gray, and when moistened with H2SO4 it colors the flame bluish green. Most specimens are strongly radioactive because of the typical thorium and uranium content. Insoluble in hydrochloric acid. After fusion with sodium carbonate, dissolve in nitric acid and add solution to excess of ammonium molybdate solution. A yellow precipitate forms (test for a phosphate) . Decomposed by heating with concentrated sulfuric acid; solution after dilution with water and filtering gives with ammonium oxalate a precipitate of the oxalates of the rare earth metals.

 

Monazite

Monazite - Brown color

 

 

Localities
The Although the mineral is fairly widespread in the rocks. it is concentrated into commercial deposits at only a few places. The most important of these are in southeastern Brazil, India, Madagascar and South Africa.  The monazite of the Brazilian Cretaceous sediments was derived from the gneisses, through which the monazite has been proved to be disseminated. The sands along the river courses of the interior are also monazitic. Brazilian monazite sand as marketed in Brazil is stated to contain about 92 percent monazite and 6.2 to 6.4 percent thoria. Another important locality for monazite is the coast of Travancore in the south of India. Along this coast, between Muttum and Colachel, monazite occurs abundantly in a naturally concentrated form, associated with ilmenite and zircon.
In the US, it has been mined from a belt 20 to 30 miles wide and 150 miles long extending along the east side of the Appalachian Mountains from North Carolina into South Carolina. The mineral has also been reported from many points in ten counties in Idaho. Near Centerville it was found with placer gold in the heavy mineral concentrates and termed "heavy yellow sand" by the miners. It may be in sufficient quantity to be of commercial importance at this location.

Industrial Uses of Monazite
Although it has been eclipsed by bastnaesite as the principal source of rare earths, Monazite is still an important rare earth ore mineral.
Monazite sands usually consist of monazite naturally concentrated with other heavy minerals, such as magnetite, rutile, ilmenite, zircon, garnet, xenotime, etc. Monazite is separated from the valueless sand in which it is found, by washing, and the residues thus resulting are further concentrated by a magnetic process. This concentration is effected by electro-magnetic separators, the magnets of which are adjusted to varying intensities. Magnetite and ilmenite are first removed, and monazite, usually the most feebly magnetic, last. Rutile, zircon, and siliceous matter pass into the reject. Using gravity, magnetism and and electrostatic separation, a nearly pure monazite product can be produced. The manufacture of rare earths and thorium chemicals from the separated monazite is a complicated and purely chemical operation. Methods using both strong acids (sulfuric) and strong bases (sodium hydroxide) have been employed to dissolve and separate the different metals present in the monazite.

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Please note that the author, Chris Ralph, retains all copyrights to this entire document and it may not be reproduced, quoted or copied without permission.

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