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
CategorySulfosalt mineral
Formula
(repeating unit)		Pb(Sb,As)2S4
IMA symbolGue[1]
Strunz classification2.HC.05a
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/a
Unit cella = 20.17, b = 7.94
c = 8.72 [Å]; β = 101.12°; Z = 8
Identification
ColorGrayish black; white with reddish internal reflections in polished section
Crystal habitAcicular crystals and anhedral grains
TwinningPolysynthetic twinning on {100}
CleavagePerfect on {001}
FractureConchoidal
TenacityVery brittle
Mohs scale hardness4
LusterMetallic
StreakBrown
DiaphaneityOpaque
Specific gravity5.2
PleochroismRelatively 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

References
  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. "Guettardite". mindat.org. Hudson Institute of Mineralogy. Retrieved October 10, 2020.
  3. Handbook of Mineralogy
  4. Webmineral data


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