This is a shaped and polished, ready to mount or display, natural Lightning Ridge opal from the mines of Australia.
It is an oval shape, polished on one side and is 12mm high, 10mm wide, 3mm thick and of 3.50 carats.
This is not a gemstone in the true sense of the word, as it is opal mixed with the matrix backing stone. The background is a mixture of semi-transparent grey crystal, with a grey streak through the centre and flashes of blue and turquoise on either side.
A totally unique stone, which would make an unusual ring/pendant or simply kept as a mineral sample.