Osmium is both the densest and the rarest element that you can dig out of the Earth. It's so hard that it's used (as an alloy) in places with constant pressure and wear, like the tips of fountain pens. One single cubic inch of this stuff weighs nearly a pound, and were you to somehow get a cubic foot of it, it would weigh over 1,400 pounds. Good luck with that, though: last year, the entire U.S. osmium production was only 165 pounds.
An amazing gallery of earth images. Looks like Christmas lights in the snow. But they are also depressing. Those lights also represent, loss of space for wildlife, diminished overall resources, rampant destruction of trees and waterways, overpopulation, loss of nighttime skies, depletion of ocean fishes, and runaway greenhouse effects. Some say, we're going through another "mass extinction", which, if true, means that even man will be cut down to a few hundred, just like last time.