Gratonite

gratonite

jordanite

canfieldite

hutchinsonite

Images

Formula: Pb²⁺₉As₄S₁₅
Valence: Pb²⁺₉As³⁺₄S^2-₁₅
Sulpharsenite [(As³⁺S^2-₃)^3-] of lead, jordanite homologous series group
Crystal system: Trigonal
Specific gravity: 6.22 measured, 6.17 calculated
Hardness: 2½
Streak: Black
Colour: Dark lead-grey
Solubility: HNO₃-stains iridescent to black; effervesces abundantly after short wait with liberation of free sulphur. Negative reaction to HCl, KCN, FeCl and KOH. Decrepitates violently and melts very easily (Mindat).
Environments

Hydrothermal environments

Gratonite occurs in vugs in hydrothermal copper ores. Associated minerals include realgar, pyrite, sphalerite, pyrrhotite, arsenopyrite, enargite, tetrahedrite, tennantite, jordanite, canfieldite and hutchinsonite (HOM).

Localities

The type locality is Excelsior Mine, Cerro de Pasco, Pasco province, Pasco, Peru.
Gratonite from Excelsior Mine - Image

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