What are lanthanides in geology ?

Lanthanides : definition

Lanthanides, also called "Rare Earth Elements", make up a set of 15 rare elements, with atomic numbers between 57 and 71, which have similar chemical properties : lanthanum, cerium, praseodymium, neodymium, prometheum (the only radioactive one), samarium , europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium.

They are usually split into light rare earths (or cerics), which range from lanthanum to samarium (57 to 62) and heavy rare earths (63 to 71), ranging from europium to lutetium.

These elements are frequently found in the same minerals, where their similar geochemical behavior allows important mutual replacement (monazite, allanite, bastnäsite...). As a result, they often share the same deposits. The rare earth elements contents are expressed in weight of oxides : Ce2O3, La2O3 or REE2O3 (Rare Earth Elements) when the different rare earth elements are not distinguished.