Osmiridium

Naturally occurring alloy of iridium & osmium, as is iridiosmium

Osmium, high durability & heaviest known element, used as part of an alloy, for fountain pen nibs, eletrical contacts, phonograph needles. Iridium, most corrosive-resistant metal known & second heaviest known element, used in an alloy for pen nibs, electrical conductors; in platinum alloys as a hardener.

When encountered by gold miners was considered a problem. Later thought, it was valuable in its own right.

Osmiridium mining started at Adamsfield in 1925, when a small town developed, until middle of the century(?).