ABSTRACT
In geochemical events the role and behavior of chemical elements depend on both their properties and their amount. Under the same conditions different elements behave differently. Dmitri Ivanovich Mendeleyev systematized the properties of elements in his periodic table of elements. In Mendeleyev's table, Fersman singled out areas corresponding to certain geochemical associations, which are in good agreement with the classification by Victor Moritz Goldschmidt. Several geochemical classifications of elements have been developed. The simplest one divides elements into petrogenic and metallogenic elements. The group of petrogenic elements includes oxygen, silicon, aluminum, calcium, magnesium, sodium, carbon, and sulfur. When investigating the behavior of a particular chemical element, a geochemist must take into account a variety of factors, including geological, chemical, biological ones. Some elements have one or two stable isotopes, whereas others have more than two stable isotopes.
