Finding opals is not the problem, they are everywhere there, finding opals with valuable color traits is the problem. It's highly random is my understanding.
I traded opals for a while, but my supply was boulder opals from around Quilpie in Queensland. Not underground like Coober Pedy and White Cliffs, but still not a whole lot there![1]
One of the best introductory books about opals is Opal Identification & Value by Paul B. Downing. It's a few years old now (latest version 2002, first published 1992), but really does cover all the basics of different types and their value very well.
