Australian Boulder Opal Ring, 925 Silver, r3Australian 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 when magnified is seen to be pitted with tiny bubbles and a spray of small gold Pyrites crystals. The veining appears blue to the naked eye but it's a clear gold without iridescence in the light box. It's a nicely made ring with the stone set in