Lyonsite

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
General
Category	Vanadate mineral
Formula	Cu3Fe+34(VO4)6
IMA symbol	Lyo[1]
Strunz classification	8.AB.40
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pmcn
Unit cell	a = 10.29, b = 17.2 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
Cleavage	Good on {001}
Tenacity	Brittle
Luster	Metallic
Streak	Dark gray
Diaphaneity	Opaque
Specific gravity	4.215 calculated
References	[2][3][4]

Lyonsite occurs as a sublimate in volcanic fumaroles. It is often associated with howardevansite and thenardite.^[2] It was first described in 1987 for an occurrence on the Izalco volcano, El Salvador. It was named for mineralogist John Bartholomew Lyons (1916–1998) of Dartmouth College.^[3] It has also been reported from a mine dump in the Lichtenberg Absetzer Mine of Thuringia, Germany.^[4]