Not all metals oxidize, tarnish, or otherwise form coatings when exposed to air. With the exception of silver, the so-called precious metals - gold, platinum, iridium, palladium, rhodium, ruthenium, rhenium, and osmium - do not react with chemicals in the air, and remain shiny and beautiful. Because of this, they are often used to make jewelry.
And these metals really are precious! Here are some typical prices for one ounce of some precious metals as of July 2011: $40 for silver (not too bad!), $800 for palladium, $1600 for gold, $1800 for platinum, and a whopping $4500 for rhenium!
The funny thing is that one metal used to be precious, but isn't any more, and that's regular old aluminum. We now make disposable cans and food containers out of aluminum (although it's always good to recycle when possible), but at one time, aluminum was more expensive than gold! In fact, in the early 1800's, the French emperor Napoleon had special flatware (forks, spoons, and knives) made out of aluminum, which he used for only his most important dinner guests. Why was aluminum so expensive? Unlike many other metals, aluminum does not occur naturally in pure metallic form. Much of is was found as alum, a mineral from which the aluminum must be separated. In Napoleon's time, this was a very long and difficult process. But in the late 1800's, an American chemist named Charles Martin Hall discovered a process that used electricity to obtain aluminum from alum cheaply and easily. Its price fell from $600 per pound in 1850 to 18 cents per pound in 1914. Hall and some partners formed the Aluminum Company of America (now Alcoa). One other interesting note about Hall - he was very young when he discovered his aluminum process. In fact, he had just graduated from college a few years before!
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