Opal Education

Australian Government - Geoscience Australia

https://www.ga.gov.au/education/minerals-energy/australian-mineral-facts/opal

Gemological Institute of America

https://www.gia.edu/search?q=opal

Australian Museum

https://australian.museum/learn/minerals/gemstones/opal/

Australian Opal Centre

https://www.australianopalcentre.com