I was reading an article about a potential worldwide shortage of iridium, a rare metal that is used in flat-screen TVs. It said (I don't have the exact quote), "Iridium, like most metals, is a good conductor of electricity. But it has the unusual property of being transparent."

Like "most" metals? I'd thought that a metal, by definition, is a substance that has certain properties including the property of being a good conductor. When I checked the dictionaries, though, I found a conflict. MW online says, "any of various ... substances that are good conductors of electricity and heat ...," but AHD says, "are generally good conductors of heat and electricity.

What's an example of a "metal" that is not a good conductor?

(And by the way, is iridium really transparent?)

We decide on metals by structure (regular cations with a delocalised sea of electrons) an by properties such as conduction of electricity. All but two of the metallic elements look pretty much the same when pure: shiny and that silvery colour.

Some non-metals have a few metallic properties, such as silicon and a few indecisve people call them semi- metals or metalloids.

Under strange conditions some familiar metals become non-metallic, for example tin turns from a hard metal to a crumbly non-metal during the Russian winter or in Antarctica, as Napoleon's officers and Robert Falcon Scott's huskies know all too well.

Under strange conditions, some familiar non-metals become metals, for example hydrogen is metallic at the centre of Jupiter.

The answer to your question might be the same as the answer to this one:

What liquid contains absolutely no water in any form?


(Not positive on this one. Just an educated guess that I'm too lazy to research at the moment. Answer in a few days.)

If you mean at normal temperatures then I would suggest mercury.

However, mercury is a very good conductor of electricity - mercury switches are in very common use, as are mercury vapour lamps.