Chalcosite is a mineral composed primarily of copper(I) sulfide, with the chemical formula Cu2S. It typically appears as dark gray to black crystals and has a metallic luster. Chalcosite is often found in hydrothermal veins and is an important ore of copper, making it significant in mining and metallurgy. This mineral can form through the alteration of other copper minerals and is commonly associated with other sulfide minerals like bornite and chalcopyrite. Chalcosite is valued for its high copper content, which can reach up to 79.8% by weight, making it a key resource in the production of copper metal.