• Question: Why do rocks generate electricity when crushed under high pressure?

    Asked by dandav to Angus, Christian, Hannah, Laura, Simon on 17 Jun 2013.
    • Photo: Christian Maerz

      Christian Maerz answered on 17 Jun 2013:

      This electricity is created by friction when two rock surfaces slide along each other. These surfaces are not completely smooth but rather uneven, so the energy that is produced between them is transformed into electricity (or electrostatic energy). It’s the same thing that happens in clouds during a thunderstorm: The friction between the water particles creates a lot of electrostatic energy that is released by lightning.

    • Photo: Simon Holyoake

      Simon Holyoake answered on 18 Jun 2013:

      not all rocks do this, one of the projects I am working on (the big press with loads of wires in my pictures) is doing just this, we are squeezing rocks to measure if they generate electrical potentials

      the exact mechanism is quite complex and mathematical, it is called the ‘piezoelectric effect’ and occurs in minerals such as quarts which have a large molecular lattice inside (all the molecules are arranged in large grids) the electrons orbiting the atoms inside this lattice are arranged in an ordered fashion. When you squeeze the material, you disrupt this order, creating a charge imbalance (each electron carries a minute electric charge) when a charge imbalance is created, you create a voltage (the negatively charged electrons are no longer spread evenly throughout the lattice, so where there are more of them, there is a higher negative charge)

      Phew, I hope that makes sense!!

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