Coober Pedy is a town in northern South Australia, 846 km north
of Adelaide. So: the correct answer is that Coober Pedy is in the
country of Australia, specifically the state of South
Australia.
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Coober Pedy in outback South Australia is known for its opals.
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The gemstone (rather than jewel) for which Coober Pedy is famous is opal.
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Coober Pedy is an opal mining town in the outback of the state of South Australia.