Monazite-(La)
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). It is also the phosphorus analogue of gasparite-(La). The group contains simple rare earth phosphate minerals with the general formula of ATO4, where A = Ce, La, Nd, or Sm (or, rarely, Bi), and B = P or, rarely, As. The A site may also bear Ca and Th.
Intro adapted from Wikipedia (CC BY-SA).
Monazite-(La) is an IMA-recognized mineral species in the phosphate class, with the chemical formula La(PO₄).
It crystallizes in the monoclinic crystal system (space group P2_1/n). It is a member of the Monazite structural group.
Key properties: Mohs hardness 5–5.5; specific gravity 5.17–5.27; [Resinous, waxy, vitreous to adamantine.] luster; optically biaxial.
IMA symbol Mnz-La, IMA status: approved, named in 1966.
Found in fissure veins, granite and gneissic metamorphic rocks.
The name refers to the member of the monazite group with dominant lanthanum.