Boulder opal is one of the most valuable varieties of opal, second only to Australia's black opal. Fine specimens of boulder opal can exhibit all of the spectral colors through their distinct play of color. Boulder opal is found embedded in large boulders of ironstone, which is how it earned its name. Occurring as pebble rock, precious opal develops within thin veins, fissures, and hollows. As opal miners attempt to remove the embedded opal from the ironstone, some of the host matrices are preserved during the process. For this reason, boulder opal is sometimes referred to as 'opal in the matrix'. The ironstone matrix enhances the stones durability and vibrancy of color. The hammered silver is on the right side, like the rock that the miner used to collect the opal and its actual natural growth conditions.