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Boulder Opal Cabochons
Boulder Opal, found in Australia where the opal forms into veins and patches within brown ironstone boulders. When opal is mixed with the ironstone it's called matrix opal. The hardness of Boulder Opal ranges between 5.5 and 6 on the Mohs scale. Boulder opal is a very durable stone because of the ironstone backing the opal forms on. If the water content within the opal is low it almost never cracks or crazes as it ages.