Question: What is the rarest material known to man

Elizabeth Cooper answered on 20 Mar 2015:

Astatine is a chemical element and this is the rarest in the world!

Scientists estimate that at a given time, less than 28 grams of astatine exists on Earth. Because it is so rare, many of astatine’s properties have been a mystery to scientists for years.

Astatine has a half life of roughly 8 hours, meaning if you could get a clump of it to stay on a table (you can’t), half of it would disintegrate in 8 hours, and then every 8 hours another half would go until in a few days, there’d be no astatine on the table. This is due to the radioactivity nature of it.