It's a mosaic triplet, which is to say it's chips of opal glued together on a dark slice of rock and then covered with quartz, but it's not well done - you shouldn't be able to see big honking gaps between the chips. It's not 'black opal' by any stretch of the imagination, either...
Here're some mosaics that are relatively well done and priced at retail - Murray's got good material, too.