[jcarrano]

It is also relatively easy to work, since ancient times. Iridium is the rarest metal, so rare and hard to work that it is not practical.

[djtango]

Yes! Exactly - there are plenty of other rare metals but many of them are really hard to work with. Iridium, Rhodium and Platinum are plenty rare but mankind has lacked the technology to do anything with them for most of history