monazite

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monazite

(mŏn`əzīt), yellow to reddish-brown natural phosphate of the rare earthsrare earths,
in chemistry, oxides of the rare-earth metals. They were once thought to be elements themselves. They are widely distributed in the earth's crust and are fairly abundant, although they were once thought to be very scarce.
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, mainly the ceriumcerium
[from the asteroid Ceres], metallic chemical element; symbol Ce; at. no. 58; at. wt. 140.116; m.p. 799°C;; b.p. 3,426°C;; sp. gr. 6.77 at 25°C;; valence +3 or +4. Cerium is a soft, malleable, ductile, iron-grey metal with hexagonal or cubic crystalline structure.
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 and lanthanumlanthanum
[Gr.,=to lie hidden], metallic chemical element; symbol La; at. no. 57; at. wt. 138.90547; m.p. about 920°C;; b.p. about 3,460°C;; sp. gr. 6.19 at 25°C;; valence +3.
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 metals, usually with some thoriumthorium
[from Thor], radioactive chemical element; symbol Th; at. no. 90; mass number of most stable isotope 232; m.p. about 1,750°C;; b.p. about 4,790°C;; sp. gr. 11.7 at 20°C;; valence +4.

Thorium is a soft, ductile, lustrous, silver-white, radioactive metal.
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. Yttrium, calcium, iron, and silica are frequently present. Monazite sand is the crude natural material and is usually purified from other minerals before entering commerce. Monazite occurs in North Carolina, South Carolina, Idaho, Colorado, Montana, and Florida in the United States, and in Brazil, India, Australia, and South Africa. It is an important source of cerium, thorium, and other rare-earth metals and compounds.

Monazite

 

a mineral; a phosphate of rare earths (mainly of the cerium group) with the chemical formula (Ce, La,…) [PO4]. It often contains various impurities, the most important of which are ThO2 (10 percent and more), UO2 (up to 6.6 percent), ZrO2, CaO, SiO2, and SO3.

Monazite crystallizes in a monoclinic system to form lamellar or sometimes thick tabular crystals, as well as irregular grains and grainy masses. The crystal structure of monazite is characterized by isolated [PO4]3− groups bonded to TR3+ ions in enneadic coordination. It is usually highly radioactive. Its color ranges from yellow or yellow-green to cinnamon and reddish brown. Hardness on the mineralogical scale, 5.0–5.5; density 4,900–5,500 kg/m3, depending on chemical composition.

Monazite deposits are usually associated with granitic pegmatites, less frequently with hydrothermal carbonate veins occurring in alkaline granites and syenites. It is extracted mainly from alluvial deposits in rivers and oceans (for example, in India, Sri Lanka, and Brazil), where it settles during erosion of granite and gneiss containing monazite as an accessory mineral. It is a raw material in the isolation of cerium and thorium.

G. P. BARSANOV

monazite

[′män·ə‚zīt]
(mineralogy)
A yellow or brown rare-earth phosphate monoclinic mineral with appreciable substitution of thorium for rare-earths and silicon for phosphorus; the principal ore of the rare earths and of thorium. Also known as cryptolite.
References in periodicals archive ?
(23) Monazite is a mineral with the formula (Ce, La, Nd,
(1999) have reported concordant U-Pb monazite ages of 1878 [+ or -] 2 Ma and an average Sm-Nd garnet age of 1870 [+ or -] 20 Ma (five Gr-Wr pairs, Mouri et al.
1778 [+ or -] 2 Ma for monazite and 1728 [+ or -] 24 Ma for garnet, are clearly younger than any comparable results from Finland.
Textural, chemical and isotopic insights into the nature and behaviour of metamorphic monazite. Chem.
Constraints on the diffusivity of Pb in monazite, its closure temperature, and its U-Th-Pb systematics in metamorphic terrains, from a TIMS and SIMS study.
The Sawara assemblyman allegedly told police investigators that he was not aware that the monazite he was holding was collateral for 5 million yen he loaned to Ikeda 15 years ago but he had no knowledge that it was monazite.
Police said the monazite was found stacked inside a storage room about 30 meters away from the assemblyman's house.
Police detected a radioactivity reading of 100 microsievert per hour nearby the monazite found in the storage room, officials said.
A sample of monazite from Llallagua, Bolivia (H110663) was also examined on the spindle stage and yielded a 2V of 25(2) [degrees] with indices of refraction equal to those reported in Palache et al.
There appears to be an effect of nuclear radiation on the optical properties of monazite. The Franklin and Llallagua non-metamict material both have 2V values near 25 [degrees].
Following the model of Cummings (1988), one may postulate the reaction of REE-containing fluid with indigenous phosphate to form monazite. The REE, Th and Y seen in the allanite are also found in the monazite, with no other REE present in the latter.
These garnet features, monazite trace-element signatures, and monazite ages suggest that prograde metamorphism was still underway at 29 Ma, but that decompression or cooling was occurring by 25 Ma, consistent with the interpretation that peak metamorphism and mid-crustal ductile extension began at ~35 Ma, was ongoing at ~23 Ma, and had ceased by ~16 Ma [Lee and Whitehouse, 2007].