Tennantite

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. 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.