This is a Boulder opal Stone which comes from the Winton Opal field of Queensland, Australia. It shows Red, Green and Purple in colour on its face but also on one side as well as a little on the back. A very nice and rather unusual stone. This could be set in silver and made into a pendant. It would not be able to be drilled as you would lose a great deal of the colour.
If you see an opal on this website that you might like to have as a pendant, please contact Peter to discuss if it is possible with that particular stone.
You also need to state if you wish to have a bail fitted or not. If you do, then you would need to be charged for the cost of metal, silver or gold.