The heaviest metal in the world is iridium. It was discovered in 1804 by Smithson Tennant of the United Kingdom. Iridium, which is a silvery-white metal of the platinum group weighs 1,414 pounds a cubic foot or roughly two-thirds of a ton. Lithium, the lightest metal, weighs 33 pounds per cubic foot.
If you could stand an elephant weighing nearly six tons at one end of a seesaw, you would need only a two-foot cube of iridium at the other end to lift the animal.