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.