Cuprostibite  (the name is formed from the addition of two words: cuprum and stibium)[3] — a very rare polymetallic mineral of the sulfide class, consisting of mixed copper and thallium stibnite (although not in all samples), sometimes with admixtures of tin and other metals, ideal formula Cu2(Sb,Tl) or Cu2Sb.

Cuprostibite was discovered in South Greenland (1964) and described in 1969 by a group of scientists, which included Evgeny Semyonov [ru], Henning Sorensen,[4] Marianna Bezsmertnaya and Evgenia Khalezova.

[6]: 26–27 In 1969, Evgeny Semyonov described the history of the discovery of the mineral in a separate book dedicated to the expedition to South Greenland and the mineralogy of this area: Cuprostibite <...> discovered by E. I. Semenov and H. Sorensen and studied by them together with M. S. Bezsmertnaya.

Cuprostibite forms opaque grains 1-2 mm in size, black, and on fresh chips steel-gray in color with a distinct violet-red tint.

According to the first detailed description of the discoverer of the mineral Evgeny Semyonov, cuprostibite forms opaque granular aggregates and small black phenocrysts no larger than 1-2 mm in size.

[5]: 29 One of the striking features inherent in cuprostibite is its ability to form the finest polymineral mixtures, the size of metal particles in which varies from several tens of microns to 100-200 Å.

The stability of such mixtures over a long geological time (at least 200-250 million years) can only be ensured by their isolated position inside dense host rocks.