Boulder opal is a variety of precious opal that forms within cracks and cavities in ironstone boulders. Unlike opal that is separated entirely from its host rock, boulder opal is characteristically left attached to its natural ironstone matrix, which becomes part of the specimen itself. This natural specimen shows opal occurring within dark brown ironstone, with small areas of opal visible across the matrix and a polished surface revealing the contrast between the two materials. This is a thumbnail-sized mineral specimen presented in a clear Perky display box measuring 1.25 inches. Locality: Comet Mine, Koroit Opal Field, Queensland, Australia You will receive the exact specimen pictured.