Gem that's much mined in Australia

OPAL

This iridescent stone, often called "the queen of gems," is known for its play-of-color and is the national gemstone of Australia.

This clue points to "OPAL," a precious gemstone famously mined in Australia, which produces about 90% of the world’s supply. The word "mined" hints at both the literal extraction of the stone and its role as the answer—since "OPAL" is "much mined" there. It’s a straightforward definition with a slight nod to the gem’s strong association with the country.