The heaviest naturally occurring element on Earth is osmium. It is a very dense material with a known density of 22.5 g.cm^-3 at 20 degrees Celsius. Osmium is slightly more dense than the element iridium.
Osmium is a metal that was discovered in 1803 by scientist Smithson Tennant. Osmium is typically categorized with other very dense, lustrous metals that are commonly known as platinum metals. Osmium is such a heavy element that it has a low reactivity to other elements. Osmium is often used to make materials that must be hard and have a powerful resistance to the effects of friction.