Nagyágite (Pb
5
Au(Te,Sb)
4
S
(5–8)
) is a rare sulfide mineral with known occurrence associated with gold ores. Nagyágite crystals are opaque, monoclinic and dark grey to black coloured.

Nagyágite
Nagyágite from Nagyág (Săcărâmb), Romania (image width: 1.5 mm)
General
CategorySulfosalt mineral
Formula
(repeating unit)
Pb
5
Au(Te,Sb)}
4
S
(5–8)
[1] or AuPb(Sb,Bi)Te
(2–3)
S
6
[2] or (Te,Au)Pb(Pb,Sb)S2[3]
IMA symbolNgy[4]
Strunz classification2.HB.20a
Dana classification02.11.10.01
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/m
Identification
ColourBlackish lead-grey; pale grey in polished section
Crystal habitTabular crystals (often bent), also massive granular, pseudotetragonal
TwinningCrossed twin lamellae observed on (001) sections
CleavagePerfect on {010}, excellent on {101}
FractureHackly
TenacityFlexible, slightly malleable
Mohs scale hardness1.5
LustreMetallic, bright on fresh cleavage
StreakBlackish lead-grey
DiaphaneityOpaque
Specific gravity7.35–7.49
PleochroismWeak
References[1][2][3]

It was first described in 1845 for an occurrence at the type locality of the Nagyág mine, Săcărâmb, Hunedoara County, Romania.[1][2]

It occurs in gold–tellurium epithermal hydrothermal veins. Minerals associated with nagyágite include: altaite, petzite, stutzite, sylvanite, tellurantimony, coloradoite, krennerite, native arsenic, native gold, proustite, rhodochrosite, arsenopyrite, sphalerite, tetrahedrite, calaverite, tellurobismuthite, galena and pyrite.[3]

References

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  1. ^ a b c Nagyágite, Mindat.org, retrieved 6 August 2022
  2. ^ a b c Barthelmy, David (2014). "Nagyagite Mineral Data". Webmineral.com. Retrieved 6 August 2022.
  3. ^ a b c Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005). "Nagyágite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved 6 August 2022.
  4. ^ 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.