Copper(II) oxide is an ionic black or brown solid that can be obtained from several different reactions. It also occurs in a steel-gray mineral form named tenorite.
Copper (II) oxide is not safe to handle without taking precautions. It is highly reactive and causes skin, blood and eye irritations. It is absorbed through the skin, where it can travel to the kidneys and liver through the red blood cells and cause a spectrum of medical problems, especially for people who cannot metabolize copper. In such cases, copper (II) oxide builds up in the tissues and organs where it causes damage.