Elemental Paragenesis

Paragenesis, Elemental

 

the regular, combined occurrence of chemical elements in minerals and rocks that formed under common conditions. The concept of paragenesis of elements is closely related to that of paragenesis of minerals. The combined occurrence of chemical elements in nature is set by the elements’ position in D. I. Mendeleev’s periodic table and by the physicochemical conditions under which minerals and rocks form. Many types of elemental paragenesis are known. It has been established that Li, Be, Ta, and W are paragenetically related to acidic igneous rocks and that Cr, Ni, and Pt are related to basic and ultrabasic rocks. The following types of paragenesis of elements are typical in ore deposits: Cu, Pb, Zn, Ag, and Au; Sb, Hg, and As; Sn, W, and Mo; Ag, Co, Ni, U, and Bi; and S, Se, and Te. The most common type of elemental paragenesis is the isomorphous entrapment of admixtures in compounds of the main chemical element, for example, the regular occurrence of admixtures of Cd, Ga, In, and Tl in zinc sulfide (sphalerite) or of Rb and Cs in potassium salts, for example, carnallite.

In 1909, V. I. Vernadskii arranged the chemical elements in isomorphous series and demonstrated that paragenesis is most evident in these series. The products of the radioactive decay of uranium, including Ra, He, and Pb, are found in uranium minerals. Specific types of elemental paragenesis exist for sedimentary rocks, mineral waters, and volcanic sublimates and gases. The study of elemental paragenesis is helpful in searching for mineral deposits and in studying the chemical composition of minerals and rocks.

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