Although these elements are not abundant by any means, but they are considered to be rare in the sense in which this word was used earlier. their sustaintial deposits have been found in several countries particularly in India, Scandinavia, USA, and Russia. The most commonly occuring lanthanoid in cverium which constitutes about 3 x 10 -9 % of earth’s crust.
Main minerals of lanthanoids are :
1. Monazite : It is most important mineral containing lanthanoids. it is essentially a lanthanoid orthophosphate. some monazite deposits contain appreciable amounts of thorium also. In some cases, thorium may be present to an extent of 30%.
It is interesting to note that elements with even atomic numbers are relatively more abundant and also have a large number of isotopes. whereas The elements with odd atomic numbers are less abundant and do not have more than two isotopes.
Promethium (Pm) (Z = 61) does not occur in nature and has been prepared artificially by radioactive disintegration.
2. Bastnaesite : It is a mixed fluorocarbonated MᴵᴵᴵCO₃F, where M is Lanthanoid (La). Monazitre and Bastnaesite have almost similar distribution of metals ( mainly Ce, La, Nd, and Pr) except that monazite contains approximately 8-10% ThO₂ and 3% ytterium earths which are almost not there in bastnaesite.
Large amount of bastnaesite minerals are found in California, Sweden and New Mexico.
3. Cerite : It contains silicates of Ce, La, Pr, Nd, and Sm and occurs in Sweden and Norway.
Some other minerals which are found in small amounts are :
1. Crthite : it contains double silicates of cerium.
2. Xenomite : it contains ytterbium and thorium.
3. Euxenite : it contains Ce, Nb, Th, and ytterbium earths.
4. Galolinite : it contains ytterbium earths Ce, Th.
InoOP Chem 