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Jalpaite crystals from Jalpa, Municipio de Jalpa, Zacatecas, Mexico (size: 3.6 x 3.5 x 3.2 cm)
Category Sulfide mineral
(repeating unit)
Strunz classification 2.BA.45
Crystal system Tetragonal
Crystal class Ditetragonal dipyramidal (4/mmm)
H-M symbol: (4/m 2/m 2/m)
Space group I41/amd
Unit cell a = 8.67, c = 11.75 [Å]; Z = 8
Color Pale metallic gray
Crystal habit Irregular and foliated masses, inclusions in other minerals
Cleavage Prismatic, good
Fracture Subconchoidal
Tenacity Sectile, malleable
Mohs scale hardness 2 - 2.5
Luster Metallic
Streak Black
Diaphaneity Opaque
Specific gravity 6.82–6.85
Pleochroism Distinct in oil, brownish gray to pure gray
Alters to Tarnishes with iridescence
References [1][2][3]

Jalpaite is a rare copper silver sulfide mineral with formula Ag3CuS2.

It was first described in 1858 for an occurrence in the Leonora Mine, Jalpa, Zacatecas, Mexico and named for the locality.[2] It occurs in low temperature hydrothermal veins at temperatures less than 117 °C (243 °F). Associated minerals include acanthite, mckinstryite, galena, sphalerite, pyrite, chalcopyrite, stromeyerite, polybasite, pearceite, tetrahedritetennantite and native silver.[1]