ABSTRACT
The elements selenium and tellurium, like sulfur, belong to group VI of the periodic table. All three have some properties in common, but selenium and tellurium, especially the latter, have some metallic attributes, unlike sulfur. Selenium and tellurium are much less abundant than sulfur in the Earth’s crust. Selenium amounts to only 0.05-0.14 ppm (Rapp, 1972, p. 1080) and tellurium to 10−5-10−2 ppm (Lansche, 1965). Both are associated with metal sul des in nature and occur in distinct minerals, for example, ferroselite, (FeSe2 ), challomenite (CuSeO3 · 2H2O), hessite (Ag2Te), and tetradymite (Bi2Te2S). Selenium occurs in small amounts in various soils in concentrations in the range of 0.01-100 ppm. High concentrations are associated with arid, alkaline soils that contain some free CaCO3 (Rosenfeld and Beath, 1964).
