@Ichijoe  
The tips of fountain pens are iridium.

@Parcly Taxel  
Very toxic, and despite its mass it vaporizes very readily. It’s commonly used to stain electron microscope samples, and the method is just to put a drop of osmium tetraxoide solution on a piece of wax paper near the samples, then put a petri dish over the top. When I was working with it the safety protocols were pretty simple. “If I drop this or you smell a garlicky odor, run.” The vapors crosslink your eyes and airway mucous membranes and turn them black. It’s possible to recover if the damage isn’t too deep yet, though crosslinked lungs don’t exchange air all that well, and you’re at least temporarily blind so getting away can be hard if there’s a big spill. It’s not too hard to store though; it attacks vegetable oil so readily that having some in the bottom of the outer container means any vapor that leaks out of the inner container gets used up. Even with a sealed inner container, the vegetable oil in the bottom would blacken in a couple of days.

Smelly you say? No wonder the Osmonds’ stink…

There was an album by Parliament called Osmium; one of its alternative titles was Rhenium. The element per se is the densest known based on X-ray crystallography measurements, but it finds hardly any use as a counterweight because (1) it’s expensive and (2) depleted uranium and lead are much cheaper.
 
Osmium tetroxide has many uses in organic chemistry as an agent to introduce diols on alkenes. There are downsides to that as well - it’s smelly (hence the name osmium), toxic and needs to be present in stoichiometric quantities if it’s going alone. Therefore we often add a catalyst with a strange name: N-methylmorpholine N-oxide.

The ball baring in Ballpoint Pens are made out of Tungsten Carbide, yes…

I thought pen nibs were Tungsten.