Rough diamonds - a means of storing value?

Some say rough diamonds are storing the highest value on the smallest space, but could they function as currency? 

There is a debate about what currency to use. Most Austrians would favour a gold based money and oppose fiat money(money created on the books only).  They argue that this will finally lead to a devaluation of currency. But what is the best means of storing value meaning purchasing power?

Are there any other opinions on this?