• Question: how long does lava take to turn into obsidian

    Asked by 349furk37 to Chris, Joanne, Kathryn, Kieran, Sarah on 15 Nov 2017.
    • Photo: Sarah Guerin

      Sarah Guerin answered on 15 Nov 2017:

      For obsidian to form, lava has to cool very very quickly so it doesn’t crystallise- from what I read this would be a few minutes!

    • Photo: Chris Werner

      Chris Werner answered on 15 Nov 2017:

      Yup, exactly as Sarah said, only a few minutes. You would usually get obsidian forming when lava cools in water. The larger crystals in a volcanic rock, the longer it takes to cool. Look at granite, blacks, whites, creams and tiny, but large crystals. Basalt on the other hand, like in Hawaii you’d need a microscope to see the crystals, usually less than 0.05 mm across, and that cools quickly too!

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