Lyonsite (Cu3Fe+34(VO4)6) is a rare black vanadate mineral that is opaque with a metallic lustre.
Lyonsite often occurs as small tabular typically well formed crystals.
Lyonsite has a good cleavage and a dark gray streak.
Lyonsite occurs as a sublimate in volcanic fumaroles.
It was named for mineralogist John Bartholomew Lyons (1916–1998) of Dartmouth College.