If memory serves me, this is the last bead from a strand of opals. Would be a "common opal", also called "potch", with no play-of-color. White, grey and black in color. Blue highlights more pronounced in the pictures, less obvious in the stone. This bead, cut into a rectangular shape, measures 30 mm x 20 mm. Wrapped in sterling silver wire.
Finished size is 45 mm x 21 mm. Weight is 0.3 oz.