Rheniite is a very rare rhenium sulfide mineral with the chemical formula (ReS2).

It forms metallic, silver grey platey crystals in the triclinic - pinacoidal class.

Almost all commercially mined rhenium is retrieved as a by-product of molybdenum mining as rhenium occurs in amounts up to 0.2% in the mineral molybdenite.

A discredited rhenium sulfide known as zappinite does not appear to be valid.

Rheniite has also been reported in the Pagoni Rachi Mo–Cu–Te–Ag–Au deposit in northeastern Greece where it occurs with molybdenite in quartz veins associated with an epithermal system in a dacite porphyry.