borniet

Borniet is a hypothetical mineral species used in mineralogical thought experiments and in some science-fiction contexts. It is described as a copper-iron sulfide with iridescent tarnish that shifts color under light.

The name is a coined term following mineral-naming conventions, with the -iet suffix common for minerals.

Reported composition is often cited as Cu5FeS4 with small substitutions of Zn, Sn, or Sb. Typical color is dark bronze with interference colors on tarnish. Mohs hardness about 4; density roughly 5.0–5.4 g/cm3.

It is described as forming in hydrothermal veins and low-sulfur, high-temperature environments; commonly associated with chalcopyrite, bornite, and magnetite, though it remains a hypothetical species.

In teaching, it illustrates how trace-element substitutions influence color and crystallography; in speculative fiction, it is imagined as a valuable copper ore or rare mineral resource.