[en] Semiquantitative eigenvector analysis demonstrates that the differentiation of individual lanthanoids occurs in sedimentary environment. By means of eigenvector diagrams, the degree of lanthanoid fractionation can be expressed semi-quantitatively. Recent papers lend support to the idea that under given circumstances, the elements of lanthanoid group (La - Yb) can be differentiated by geological processes. In the present study, eigenvector analysis was used for the investigation of the behaviour of lanthanoid elements in clays and bauxites. The material for the present study was three series of samples. Two of them were clays derived from the same geological source area, and they were different mainly by the natural conditions under which they had been deposited. The third sample set was bauxite, so rich in hematite that it is nearly iron ore with economic value. (J.P.N.)