Occurs in nature as the mineral berzelianite which in addition to copper and selenium contains 4.73-8.50% silver, 0.35-0.54% iron, up to 0.38% thallium and traces of lead and magnesium. Prepd by reduction of an ammoniacal soln of a cupric salt and H2SeO3 with hydrazine: Benzing et al., J. Am. Chem. Soc. 80, 2657 (1958); Kulifay, J. Inorg. Nucl. Chem. 25, 75 (1963); alternate methods: Glemser, Sauer in Handbook of Preparative Inorganic Chemistry vol. 2, G. Brauer, Ed. (Academic Press, New York, 2nd ed., 1965) p 1019.