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Category Vanadate mineral
(repeating unit)
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
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 [1][2][3]

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.[1] 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.[2] It has also been reported from a mine dump in the Lichtenberg Absetzer Mine of Thuringia, Germany.[3]