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A sample of tennantite
Category Sulfosalt minerals
(repeating unit)
Strunz classification 02.GB.05
Color Flint-gray to iron-black, cherry-red in transmitted light
Crystal habit massive to well formed crystals
Crystal system Cubic Hextetrahedral H-M Symbol (43m) Space Group: I 43m
Twinning Contact and penetration twins
Cleavage None
Fracture Subconchoidal to uneven
Tenacity Somewhat brittle
Mohs scale hardness 3 - 4.5
Luster Metallic, commonly splendent
Streak reddish gray
Diaphaneity Opaque, except in very thin fragments
Specific gravity 4.65
Polish luster gray, inclining to black to brown to cherry-red
Optical properties Isotropic
Refractive index n greater than 2.72
References [1][2][3]

Tennantite is a copper arsenic sulfosalt mineral with an ideal formula Cu12As4S13. Due to variable substitution of the copper by iron and zinc the formula is Cu6[Cu4(Fe,Zn)2]As4S13.[1] It is gray-black, steel-gray, iron-gray or black in color. A closely related mineral, tetrahedrite (Cu12Sb4S13) has antimony substituting for arsenic and the two form a solid solution series. The two have very similar properties and is often difficult to distinguish between tennantite and tetrahedrite. Iron, zinc, and silver substitute up to about 15% for the copper site.[1][2]

The mineral was first described for an occurrence in Cornwall, England in 1819 and named after the English chemist Smithson Tennant (1761-1815).[1]

Tennantite from Ireland

It is found in hydrothermal veins and contact metamorphic deposits in association with other Cu–Pb–Zn–Ag sulfides and sulfosalts, pyrite, calcite, dolomite, siderite, barite, fluorite and quartz.[2]

See also[edit]