Rheniite is a very rare rhenium sulfide mineral (ReS2). It forms metallic, silver grey platey crystals in the Triclinic - pinacoidal class. It has a specific gravity of 7.5.

It was discovered at the Kudriavy Volcano, Iturup Island in the Kurile Islands, Russia and approved in 2004. It is found in active hot fumaroles on the volcano.

Rheniite is the only known mineral of the element rhenium. 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.