Bornite

Bornite is a mineral that is found in several areas of the world, but was first described in the 1700s in the Bohemian region of present day Czechia. Composted of the elements copper, iron, and sulphur — chemical formula: Cu₅FeS₄ — it is an important ore of copper. This rock feels ever-so-slightly heavy for its size; not remarkably heavy, but just a bit, because of the copper and iron it contains.

Bornite naturally ranges from brown to reddish-brown in color. But, because this mineral is composed primarily of copper and iron, both of which oxidize readily, bornite has the tendency to tarnish easily. When that happens, it can turn beautiful, almost iridescent colors with patches of blue, green, gold, and pink. This property has earned it the fitting name of "Peacock Ore." The following photo shows the same piece of bornite pictured above, but with oxidation present.

In some specimens, the oxidized colors can be even brighter!

The same oxidation process is often seen in statues and domes of buildings which have been constructed of copper or bronze. The following photo of Kaiser Wilhelm I — King of Prussia, the first German Emperor, and the first Head of State of a united Germany — illustrates this greenish tarnish, which is referred to as verdigris (pronounced: VER' - duh - gree, as it is a word borrowed from the French, and the ending "s" is silent). The grayish areas on the statue are the original color, and the green patina is the verdigris.

What I call the reverse ("back") side of my bornite specimen has splotches of magenta, vivid pink, and aqua, which were much more pronounced when I got the stone a decade or so ago. I suppose I should put it outside, let it oxidize again, and re-shoot it... LOL! 😁