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    how is an opal formed

    0  Views: 219 Answers: 1 Posted: 14 years ago

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    Opal is formed from a solution of silicon dioxide and water. As water runs down through the earth, it picks up silica from sandstone, and carries this silica-rich solution into cracks and voids , caused by natural faults or decomposing fossils. As the water evaporates, it leaves behind a silica deposit. This cycle repeats over very long periods of time, and eventually opal is formed.


    http://www.opalsdownunder.com.au/learn-about-opals/advanced/how-opal-formed-geology-opal



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