Opal is the October birthstone. Most people think of the white Australian variety when they think of opal; however opal comes in many colors and from many places. Opal is formed over a very long period of time from water and silica flowing into the cracks of rocks and hardening. In addition to white Australian opal, there is black and grey Australian opal as well. Most of the Australian opals are called precious opal, which means they have a play of color that has different spectral colors that change with the viewing angle of the opal. Opals without a play of color are called common opa...
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