Latitude -30.851794, Longitude 143.085236
Located in the Outback Region of NSW, nearest town White Cliffs
Source: www.resources.nsw.gov.au/geological White Cliffs 1:250,000 Explanatory Notes
At White Cliffs opal is found in Lower Cretaceous age claystone belonging to the Rolling Downs Group. The claystone is of marine origin and opalised shells and fossils of fish and marine reptiles such as ichthyosaurs and plesiosaurs have been found by opal miners. The opal is not concentrated in any one horizon, but occurs spasmodically throughout the Lower Cretaceous claystone. It occurs as thin horizontal and vertical veins, as irregular nodules, as wood opal, replacing shells and as crusts on boulders.
White Cliffs is the only place where "pineapples" occur; they are a pseudomorph of Glauberite or Ikaite crystal clusters, where crystals are substituted by precious opal. This results in an object where the appearance and dimensions look like crystals, but the original mineral has been replaced by opal. They are extremely rare and valuable.
Opal is formed from a solution of silicon dioxide and water. As water runs down through the earth, it picks up silica from sandstone and carries this silica-rich solution into cracks and voids or decomposing fossils. As the water evaporates, it leaves behind a silica deposit. This cycle repeats over very long periods of time and eventually opal is formed.
White Cliffs was Australia's first commercial opal field with intensive opal mining beginning in 1889. Most work in the field was done in the first 20 years. The opal from White Cliffs is known as "white opal" in contrast to the "black opal" of Lightning Ridge.
Some of the best locations were: The Blocks Area where there was no hard silcrete cover to dig through to get to the opal bearing zone and quality opal was found down to a level of 24m; Sullivans Hill to the east of The Blocks and on the margin of outcrops of the Cretaceous, most of the activity took place near the scarp where silcrete and ironstone gravels were not prominent and levels were worked down to 12m; Other areas were Turleys Hill, Smiths Hill, Moffatts Hill and many others.
There are many opal showrooms to explore in White Cliffs, plus you can spend a night or many in the world's largest underground motel or in a underground B&B. If you don't want to sleep underground there is the hotel/motel or the caravan park. While in town consider taking a trip out to Paroo Darling National Park to see the mound springs (see article on this website).
To get to White Cliffs turn north off the Barrier Highway at Wilcannia, midway between Broken Hill and Cobar. Travel on a fully sealed road one hour - 93km north to White Cliffs.