This piece of Australian Boulder opal is from the Koroit area. We didn't pick it but we did buy it from the folks that did over at two skies. We have a few pieces set aside to cut and polish, and a couple of pieces like this, loose, rough opal for sale.
This opal crystal has deep blues throughout a thicker top layer. There is a hint of green in the vein. The vein on top runs into the boulder itself so there is a surprise waiting for whoever cuts it open. It has a second vein running into the rock at the bottom, too.
There is  potential for making money from this opal if you know how to cut it. We are a little nervous to approach lapidary work on opals, but we'll work up to it. 
This piece differs from the other listed. It has an opal crack running through the middle in blue and green.
This opal crystal on boulder will make a lovely display piece in any crystal collection. 
There's a lovely legend from the Aboriginal people about how the Gods made the world. When they were done, they put all the leftover colours into the opals. It's one of our favourite crystal stories.
In terms of healing, crystals like opal are renowned for a somewhat chaotic energy. This earned them the reputation of being bad luck to wear. If you liked Moldavite, you will love opal.