Australian Boulder Opal Ring, 925 Silver, r1Australian Boulder Opal Ring 925 Silver Boulder Opal is generally an Ironstone Matrix rock with veins of Opal running through. Matrix in this case means the Mother or Host rock. In this example that host rock is pitted with tiny bubbles that have a gold play under magnification, possibly Pyrites. There's no obvious iridescence here, but the veins appear blue to the eye in normal light yet very clear and gold in colour in the magnified photos of the