Osmium

Osmium is a hard, bluish-white platinum group transition metal that can be found as a trace element in alloys and platinum ores. This is one of the most expensive precious metals.

Osmium's the densest naturally occurring element, and it's used to manufacture fountain-pen nibs and electrical contacts. It's also one among the world's rarest elements, which explains why it commands such a premium price.

You should expect to pay roughly $400 per troy ounce, which has remained fairly steady throughout the 1990s but can fluctuate slightly depending on the market.

Price: $400 per troy ounce