Fettelite is a mercury-sulfosalt mineral with the chemical formula Ag₁₆HgAs₄S₁₅. The mineral was first described by Wang and Paniagua (1996) who named it after M. Fettel, a German field geologist who collected the first samples from Odenwald. It was first collected in the Nieder-Beerbach mine, 10 km south of Darmstadt, Odenwald, Germany. Its normal occurrence is in hydrothermal veins, which can cut gabbro-diorite intrusives. It is closely related to other rare minerals like dervillite, daomanite, vaughanite and criddleite which are also found in the same type locality as fettelite.