This piece of Australian Boulder opal is from the Koroit area. We didn't pick it but we did but it straight from the source through Two skies at the British gold panning championships. We have a few pieces set aside to cut and polish, and a couple of pieces like this, loose, partially polished boulder opal for sale.
This opal has a lovely coloured patch in the centre which is evident in the pics. What you maybe can't see are the veins of opal, mainly blue to purple, which run around the outer layers.
This piece of opal has a second, smaller vein jutting into the boulder on the opposite end. 
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.