Fettelite, also known as sanguinite, 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. Its normal occurrence is in hydrothermal veins , which can cut gabbro. It is closely related to other rare minerals like dervillite , daomanite which are also found in the same type locality as fettelite.
Fettelite occurs as clusters of hexagonal flakes. These flakes can get up to 0.2 mm across and around 5-10 µm thick. In more complex hexagonal tablets, somewhat larger sub parallel aggregates can be measured. The birefringence of Fettelite is moderate white to grayish brown.