• Question: Volcanoes can create crystals and diamonds, step by step can you tell me the process of this procedure?

    Asked by littlemisstiger to Davie, Gemma, James P, James V, Nuala on 3 Jul 2012.
    • Photo: James Pope

      James Pope answered on 3 Jul 2012:


      Hi littlemissstiger,

      To my knowledge, Diamonds are only created deep underground in a rock called Kimberlite, which is formed under high temperature and pressure to create diamonds. The crystals created when a volcano erupt are all caused by the cooling of the erupted lava (and also any magma that doesn’t get erupted).

      In the magma, are all sorts of chemical elements in their liquid form, such as silica, aluminium, iron, magnesium and calcium. When the magma is erupted is leaves the super heated magma chamber and starts to cool. As it cools, the chemical elements react with each other and oxygen in the air to form crystals, such as Quartz (SiO2 – one silica and two oxygens). The quicker the cooling of the lava, the less time there is for minerals to form and so you get rocks that have less crystals, if the lava takes a long time to cool down, then you get rocks containing all sorts of crystals such as Olivines, Pyroxenes and otehr minerals.

      As the chemistry of the magma varies, so does the type of crystals you get from the cooling process, and the type of crystals and chemistry of the magma determines what sort of Igneous (volcanoic) rock you get. So in summary, the speed of cooling and the chemistry of the magma determine the type of crystals you get.

    • Photo: James Verdon

      James Verdon answered on 3 Jul 2012:


      HI little misstiger,
      I think James P sums it up pretty well here. Diamonds, which are pure carbon, can only form under huge pressures. These pressure are only reached at the very base of our crust.

      However, volcanoes can be important for moving the diamonds from the deep crust to a place where we can reach them. Kimberlites are a type of volcano that brings up molten material from the very base of the crust (we do not currently have any active kimberlite volcanoes on the planet, they are all now extinct). So the diamonds are brought up to the surface because they get caught up in the kimberlite magma as it rises.

      The more common volcanic crystals are formed, as James P says, by the slow cooling of the molten material, which crystalises as it cools (just like ice crystalises when you freeze water).

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