You may have heard that a U.S. penny is now worth more than one cent. Why? It's not the zinc filling, to be sure. It's the precious red coating of copper that imparts monetary value — as well as esthetic value when inserted in loafers.

Copper was called aes Cyprium in Roman times, after mines in Cyprus where the metal was found in abundance. Associated with the goddess Aphrodite (most likely for its use in mirrors) the symbol for Venus ♀ is also copper's alchemy symbol.

The politics of copper

After Chile, the U.S. is the second largest producer of copper. Others are Indonesia, Australia, Russia, and China. Though copper carbonates and oxides exist in nature, most ore is mined as sulfides from large, open-pit mines. These pits are copper's major environmental drawback; the arsenic and sulfur they expose can make for contamination and acid pools. One such abandoned pit in Montana contains 80 billion gallons of acid, accumulated from leaching water.

According to the American Copper Development Association, the copper industry is largely fragmented today, with most companies producing a single product or form of copper. In 1967, Chile, Peru, Zambia, and Zaire, formed an Intergovernmental Council of Copper Exporting Countries, attempting to play a role similar to that of OPEC. However, the U.S. never joined, and the group went defunct.

Alloy polloi

Originally, man smelted and used pure copper. It began as the Neolithic era gave way to the Chalcolithic, during which all-copper tools were used alongside stone. But then came the Bronze Age: As soon as man discovered the benefits of alloying copper (2,500 BC or so) the material drove civilization's development for a thousand years.

Bronze is an alloy of copper and tin, but it's also a generic term for aluminum, manganese, and silicon copper alloys. Other useful alloys include Monel (copper and nickel) and brass — copper and zinc.

One metal, many colors

Even liquid copper has a red luster. Why? Its energy band structure absorbs hues complimentary of red in the visible spectrum with electrons sitting near those photon energies — and reflects red-orange wavelengths of λ ≈ 650 to 680 nm unused. The shine of the metal is due to its free electrons, which reflect a portion of any incidental white light without scattering.

But what about the brilliant green ions of Cu+1 and stable Cu2+? In the presence of other atoms, electrons in copper's partially filled d orbital are repulsed outward (to two energy levels) by the ‘visiting’ electrons; energy from photons at the right mode are subsequently absorbed, promoting the copper electrons from the lower to the higher energy level. The same phenomenon is at work in blue copper sulfate, often used as a fungicide, and the copper-based oxygen carriers in blue mollusk blood.

King of conduction

As far as pure metals go, only silver has higher conductivity, its electrons being more readily available to conduct current. For this reason, most systems carrying electricity use copper — from delicate electronics and communication lines to heavy-duty motors and power supplies.

Copper also is increasingly replacing aluminum in heatsinks because of its superior heat conductivity and dissipation. And because bacteria don't grow on biostatic copper, it's also used in plumbing.