Guettardite

Guettardite is a rare arsenic-antimony lead sulfosalt mineral with the chemical formula Pb(Sb,As)₂S₄. It forms gray black metallic prismatic to acicular crystals with monoclinic symmetry. It is a dimorph of the triclinic twinnite.

Guettardite
General
Category	Sulfosalt mineral
Formula	Pb(Sb,As)2S4
IMA symbol	Gue[1]
Strunz classification	2.HC.05a
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/a
Unit cell	a = 20.17, b = 7.94 c = 8.72 [Å]; β = 101.12°; Z = 8
Identification
Color	Grayish black; white with reddish internal reflections in polished section
Crystal habit	Acicular crystals and anhedral grains
Twinning	Polysynthetic twinning on {100}
Cleavage	Perfect on {001}
Fracture	Conchoidal
Tenacity	Very brittle
Mohs scale hardness	4
Luster	Metallic
Streak	Brown
Diaphaneity	Opaque
Specific gravity	5.2
Pleochroism	Relatively strong
References	[2][3][4]

Discovery and occurrence

It was first described in 1967 for an occurrence in the Taylor Pit, Madoc, Hastings County, Ontario, Canada. It was named for French naturalist Jean-Étienne Guettard (1715–1786).^[2]

It occurs in hydrothermal veins within marble at the type locality in Modoc. It occurs associated with pyrite, sphalerite, wurtzite, galena, stibnite, orpiment, realgar, enargite, tetrahedrite, zinkenite, jordanite, bournonite, sterryite, boulangerite, jamesonite and sartorite at Madoc.^[3]

In addition to the type locality, it has been reported from the Brobdingnag mine, near Silverton, Colorado; the Jas Roux deposit in Hautes-Alpes, France; from various marble quarries near Seravezza, Tuscany, Italy; a marble quarry in Valais, Switzerland and from Khaydarkan, Fergana Valley, Alai Mountains, Kyrgyzstan.^[2][3]

See also

• List of minerals named after people