Last night one rough Koroit rock went for $300 but the cut gem from it would have readily fetched $1,000. Right now good "boulders" are going for 20 to 60 dollars. small bean gems called Cabs are plentiful but I only want to create large 3 inch broach sized dislays.
While the DARK semi translucent sparkling color gems go for 5 or six figures I feel that the painted rock in which Koroit opal is dispersed makes a far more interesting display. Harlaquin is one term applied to some of the multicolor stones.
of course after polishing, Koroit black opals look even more intriging but even if a piece has scant few opals the designs in the rock matrix is my favorite. I have 3 rich wood colored slabs that are virtually all matrix but the accidental landscape or faces they form are more valuable to me than digging out a fleck of violet blue opal. In fact if an opal does not create a noticable portrait or emotional image, I resell them in a heart beat.
Koroit is in Oz, The other Aussie hot spots are Queensland and (Coober Peddy?). Oh crap I just dropped my submarine sandwich...
Now I have to buy some diamond paste in various grit. Good advioce, don't mix your grits,