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Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. [3] The most common species of the group is monazite-(Ce), that is, the cerium-dominant member of the group. [4] It occurs usually in small isolated crystals.
The mineral assemblage formed by metamorphism depends on the composition of the parent rock and more importantly, the stability of different minerals at varying temperature and pressure (P-T). A set of mineral assemblages that form under similar temperature and pressure is called a metamorphic facies .
It is the cerium-dominant analogue of monazite-(La), monazite-(Nd), and monazite-(Sm). It is also the phosphorus analogue of gasparite-(Ce). [3] The group contains simple rare earth phosphate minerals with the general formula of AXO 4, where A = Ce, La, Nd, or Sm (or, rarely, Bi
Monazite has characteristics of high closure temperature (>1000 °C), variable composition, and robustness under a large temperature range, which help in the record of geological history in metamorphic rocks. [32] An electron microprobe is usually used for the measurement of monazite composition. [33]
The principal sources of rare-earth elements are the minerals bastnäsite (RCO 3 F, where R is a mixture of rare-earth elements), monazite (XPO 4, where X is a mixture of rare-earth elements and sometimes thorium), and loparite ((Ce,Na,Ca)(Ti,Nb)O 3), and the lateritic ion-adsorption clays.
Monazite is considered a diagnostic accessory mineral of S-type granites, whereas allanite is diagnostic of I-type granites. Oxide minerals in S-type granites will more commonly be ilmenite rather than magnetite. [1] [4] Accessory minerals in S-type granites commonly are associated with, or occur as inclusions, in biotite.
The source rocks which provide the heavy mineral sands determine the composition of the economic minerals. The source of zircon, monazite, rutile, sometimes tungsten, and some ilmenite is usually granite. The source of ilmenite, garnet, sapphire and diamond is ultramafic and mafic rocks, such as kimberlite or basalt.
Monazite-(Sm) is an exceedingly rare representative of the monazite group, with samarium being the dominant rare earth element in its structure. It is the samarium analogue of monazite-(Ce), monazite-(La), and monazite-(Nd). It is only the second known mineral with samarium being the mineral-forming element, after florencite-(Sm). [3]