tenorite

Tenorite is the mineral form of copper(II) oxide, with the chemical formula CuO. It is a black to dark brown oxide that occurs in the oxidized zones of copper-bearing ore deposits and in hydrothermal veins, typically as an alteration product of primary copper sulfides such as chalcopyrite and bornite, or as a secondary phase in copper oxide and carbonate assemblages.

In hand specimens tenorite is black with a submetallic to dull luster; the streak is gray to gray-black and it is opaque. Crystallography places tenorite in the monoclinic system, and it is most often found as fine crystals, tabular plates, or compact masses rather than well-formed crystals.

Typical physical properties include a Mohs hardness around 3.5 to 4 and a specific gravity near 6.0. It is commonly associated with other copper minerals such as malachite, azurite, chrysocolla, and cuprite.

Tenorite is relatively uncommon and is not a major copper ore; copper metal is produced from more economically abundant sources. It is of interest mainly to mineral collectors and researchers studying the oxidation zones of copper deposits.