Friday, February 1, 2013

Malachite – Cu2CO3(OH)2

So – you and your Neolithic buddies are sitting around the campfire, a fire pit lined by white rocks and a couple funny green and black ones thrown on for good measure. Throw some more rocks over them, some slabs to roast meat on, and more wood – that’ll heat up the place. In the morning while going through the coals for leftover meat scraps that fell off in the evening before, hey – what’s this? A bright shiny red material, sort of soft, you can hammer it and bend it, maybe it can be used as an arrowhead or even some pretty beads for your mate –why not?

Voila, the Copper Age.

Like gold, copper does occur as a native metal naturally. Though rare, native copper provided the basis of a valuable ornamental commodity back in early Neolithic times (about 8000 years ago). But then, as the preceding scenario shows, if some of those green rocks (containing malachite) got into a fire that was just a bit hotter than a normal campfire (say, ~ 700°C instead of ~600 - 650°C of a friendly campfire), and if those white rocks were limestone to help introduce some carbon into the system, then chemistry takes over: the heated malachite first degrades to a copper oxide, then can react with carbon to reduce to metallic copper.

At this historic point, copper can be, well, essentially mass produced. With a reliable “inexpensive” supply of malachite ore, copper became used more for real tools rather than hoarded as jewelry. Oetzi, the 5300 year-old frozen man found in the Alps, carried an axe with a copper blade derived from malachite ore. The elemental symbol for copper, Cu, is derived from the name of the island of Cyprus where much early production of copper from malachite occurred. Perhaps one of the most impressive sites worldwide for ancient copper mining based on malachite and azurite (another copper carbonate ore) is the Great Ormi Mine in Wales.

Technology progresses, even in the Neolithic: at sometime around 3000 years ago, procedures for reducing copper from chalcopyrite were discovered and proper smelting of ores began, a process needing temperatures capable of melting rocks as well as adding strong blasts of air (that is, oxygen) over the mix. Though malachite certainly continued to be processed, the miners’ target switched to chalcopyrite. Even today, following scraps of malachite in streams to sources of chalcopyrite is still an explorationist’s tool.

Malachite in our modern world is cherished in its own right by collectors and in jewelry. As a “healing stone,” it is said to reflect love, loyalty, aid eyesight and toothache, ward off nightmares, and aid business success. For whatever reasons, quality malachite is now worth much more than the copper it once produced.

Photo: malachite from exploration for copper ores in Greece.

To further “get into” the subject:

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