Rough opals come from different locations in Australia. The miners will sort rough and grade it according to what is visible on the outside.
A pile of rough can vary in price depending on what the miner thinks is in it.
Buying rough can be a little bit risky. One stone might be all you find that can be cut and polished, sometimes none. If you are lucky, this stone might be a good one and fetch good money. Sometimes there is more than one.
If you are not a jeweler/cutter, it is best that you check how much it will cost to cut and polish an opal before you buy.
Some rough is beautiful as is without cutting, and collectors will make sure to preserve it uncut.