Atomic number: 76

Symbol: Os

Category: transition metal

Density at 25°C: solid: density: 22.59 g·cm−3

Often found naturally alloyed with platinum, this element is used where durability is important. For example it has been used in the nibs of fountain pens. It's also the densest naturally occurring element. Though it's oxide tends to be quite toxic. 

99.99% osmium crystal. image: adapted from wikipedia

Use, natural applications or common combinations: 

  • electrical contact points
  • stains for samples of cells for electron microscopes 
  • pen nibs
  • was once used in lighting. The lighting company name Osram is a combination of osmium and wolfram.

Basic characteristics:

  • Standard atomic weight: 190.23(3)
  • Melting point: 3033 °C
  • Boiling point: 5012 °C
  • Radioactivity: almost all naturally stable
  • 186Os is very slightly radioactive releasing an alpha particle