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Monazite was the only significant source of commercial lanthanides, but because of concern over the disposal of the radioactive daughter products of thorium, bastnäsite came to displace monazite in the production of lanthanides in the 1960s due to its much lower thorium content.
Monazite geochronology can also reveal igneous differentiation events such as magma mixing, where the magma chamber is evolved into a different composition. Isomorphous substitution is one of the examples. It is a form of substitution in which one element is replaced by another without changing the crystal structure.
Huttonite is isostructural with monazite. Substitution of the rare-earth elements and phosphorus of monazite with thorium and silicon of huttonite can occur to generates a solid solution. At the huttonite end-member, continuous rare-earth substitution of thorium of up to 20% by weight has been observed.
The composition of the lanthanides was about 49% cerium, 33% lanthanum, 12% neodymium, and 5% praseodymium, with some samarium and gadolinium, or distinctly more lanthanum and less neodymium and heavies as compared to commercial monazite. The europium content was at least double that of a typical monazite.
In the study of metamorphic petrology, uranium–thorium–lead dating of monazite (monazite geochronology) is an effective method to determine the P-T history. [ 29 ] [ 30 ] Monazite is a phosphate mineral containing light rare-earth-elements (LREE) that occurs in a wide range of rock types. [ 31 ]
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.
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), and X = P or, rarely, As.
Monazite-(La) is a relatively rare representative of the monazite group, with lanthanum being the dominant rare earth element in its structure. As such, it is the lanthanum analogue of monazite-(Ce) , monazite-(Nd) , and monazite-(Sm) .