The Andamooka Opal is a famous opal which was presented to Queen Elizabeth II in 1954 on the occasion of her first visit to South Australia. It was discovered in Andamooka, South Australia, an historic opal mining town.
The opal was cut and polished by John Altmann to a weight of 203 carats (40.6 g). It displays a magnificent array of reds, blues, and greens and was set with diamonds into an 18 karat (75%) palladium necklet.
References
Andamooka Opal Wikipedia(Text) CC BY-SA