Lyonsite

Lyonsite
General
Category	Vanadate mineral
Formula (repeating unit)	Cu3Fe+34(VO4)6
Strunz classification	8.AB.40
Crystal symmetry	Orthorhombic dipyramidal H-M symbol: (2/m 2/m 2/m) Space group: Pmcn
Unit cell	a = 10.29 Å, b = 17.2 Å, c = 4.91 Å; Z = 2
Identification
Color	Black; creamy white in reflected light in polished section
Crystal habit	As euhedral flattened lath shaped crystals
Crystal system	Orthorhombic
Cleavage	Good on {001}
Tenacity	Brittle
Luster	Metallic
Streak	Dark gray
Diaphaneity	Opaque
Specific gravity	4.215 calculated
References

Lyonsite (Cu₃Fe⁺³₄(VO₄)₆) is a rare black vanadate mineral that is opaque with a metallic lustre. It crystallizes in the orthorhombic crystal system. 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 is often associated with howardevansite and thenardite. It was first described in 1987 for an occurrence on the Izalco volcano, El Salvador. It was named for mineralogist John Bartholomew Lyons of Dartmouth College. It has also been reported from a mine dump in the Lichtenberg Absetzer Mine of Thuringia, Germany.