Opal is a silica-based gemstone that occurs all over the world.

The discovery of opal at most fields worldwide follows a similar pattern, wherein the opal is first found by someone who is unaware of its importance, followed by a period of years (or decades) before the gemstone is recognised for its value and mining begins in earnest.

Opal discovery timeline:

400BC: Dubnik; Slovakia
850: Querétaro; Mexico
1841: Barossa Valley; South Australia; Australia
1853: Erandique; Lempira; Honduras
1863: Beechworth; Victoria; Australia
1855: Querétaro; Mexico (modern rediscovery)
1872: Barcoo; Queensland; Australia
1873: Angledool (Lightning Ridge); New South Wales; Australia (discovery)
1869: Listowel Downs; Queensland; Australia
1881: White Cliffs; New South Wales; Australia (discovery)
1889: White Cliffs; New South Wales; Australia (mining commences)
1893: Opal Butte; Oregon; USA
1900: Panther Creek; Idaho;, USA
1901: Tintenbar; New South Wales; Australia (discovery)
1903: Lightning Ridge; New South Wales; Australia (mining commences)
1905: Virgin Valley; Humboldt County; Nevada; USA
1915: Coober Pedy; South Australia; Australia
1919: Tintenbar; New South Wales; Australia (mining commences)
1921: Mintabie; South Australia, Australia
1930: Andamooka; South Australia, Australia
1948: Spencer; Idaho; USA
1967: Labaak, Bengkulu, Sulawesi; Indonesia
1970: Pedro 2 Mine; Brazil
1989: Arizona, Louisiana; USA
1993: Mezezo; Shewa; Ethopia