Locality: Siglo Veinte Mine (Siglo XX Mine; Llallagua Mine; Catavi), Llallagua, Rafael Bustillo Province, Potosí Department, Bolivia (Locality at mindat.org).

Monazite-(Ce) (CePO4) is the most common representative of the monazite group.

It is also the phosphorus analogue of gasparite-(Ce).

[2] The group contains simple rare earth phosphate minerals with the general formula of AXO4, where A = Ce, La, Nd, or Sm (or, rarely, Bi), and X = P or, rarely, As.

The A site may also bear Ca and Th.