Opal is composed of fragile layers of silica and derives its colour from the refraction of light – characteristics that preclude the use of heavy mining machinery, as one false blow would break the matrix and destroy the colour. Deposits are patchy and located by trial and error: the last big strikes at Coober Pedy petered out in the 1970s, and though bits and pieces are still found – including an exceptional opalized fossil skeleton of a pliosaur (the reptilian equivalent of a seal) in 1983 – it’s anybody’s guess as to the location of other major seams (indeed, there may not be any at all).
Unless you’re serious (in which case you’ll have to buy a Miner’s Permit from the Mines Department to peg your 50m-by-50m claim), the easiest way to find something is by noodling over someone’s diggings – ask the owner first. An area on the corner of Jewellers Shop and Umoona roads has been set aside as a safe area for tourists to poke about freely without danger of finding open mine shafts. Miners use ultraviolet lamps to separate opal from potch (worthless grey opal), so you’re unlikely to find anything stunning – but look out for shell fossils and small chips.
The best time to buy opal is outside the tourist season, but with about fifty dealers in town, it’s up to you to find the right stone; reputable sources give full written guarantees.