This is a shaped and polished, ready to mount or display, natural Lightning Ridge opal from the mines of Australia.
It has an oval shape and is approx. 13mm by 8mm, 3.5mm thick and of 2.95 carats.
This opal has an olive grey background colour, with flashes of red, green, yellow and blue across its surface.
A totally unique large stone, which would make an unusual ring/pendant or simply kept as a mineral sample.