Monazite-(Ce)

phosphate

cerium mineral

Monazite-(Ce) is the overwhelmingly most common member of the monazite group. Formula: Ce(PO4) phosphate
Specific gravity: 5 to 5.5
Hardness: 5 to 5½
Streak: White
Colour: Commonly reddish brown to brown; shades of green to brown, yellow brown, rarely nearly white; yellow, colourless in transmitted light.
Solubility: Slightly soluble in hydrochloric, sulphuric and nitric acid
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites
Sedimentary environments
Metamorphic environments
Hydrothermal environments (infrequent)

Monazite is a comparatively rare mineral occurring as an accessory in some plutonic igneous rocks, in pegmatites and as rolled grains in sands because of its resistance to chemical attack and its high specific gravity.
It may be found in granite including aplite, syenite, schist, gneiss and granulite.
In clastic sedimentary deposits it is associated with other resistant and heavy minerals such as magnetite, ilmenite, rutile and zircon.
At Llallagua, Bolvia, monazite occurs both as an igneous mineral, with a high thorium content, and also as a hydrothemal mineral, with a characteristically low thorium content. It is associated with fluorapatite, other hydrous phosphates and cassiterite. As the temperature drops, monazite begins to crystallise out at about 550oC and continues on down to about 300oC, when most of the cassiterite crystallises.

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