Lyonsite (Cu 4)6) is a rare black vanadate that is opaque. It crystallizes in the orthorhombic crystal system. Lyonsite often occurs as small tabular typically well formed crystals and a dark gray streak.
Lyonsite occurs as a sublimate fumaroles. It is often associated with howardevansite It was first described in 1987 for an occurrence on the Izalco volcano. It was named for mineralogist John Bartholomew Lyons (1916–1998) of Dartmouth College It has also been reported from a mine dump in the Lichtenberg Absetzer Mine of Thuringia