Igneous rocks - formed deep in the Earth's mantle and then spewed out of volcanoes - contain beautiful microscopic crystal structures not visible to the naked eye.

These colourful collages - seen with a polarising microscope - are being used by scientists trying to gain better understanding of what the interior of the Earth is like hundreds of kilometres beneath us.

John Maclennan from the University of Cambridge's Department of Earth Sciences explains how a vast rock collection at the city's Sedgwick Museum - amassed by a geologist who lived more than a hundred years ago - could hold the key.

All images subject to copyright. Images courtesy University of Cambridge, Getty Images and Science Photo Library.

Music by KPM Music. Photofilm by Paul Kerley.

Related:

Sedgwick Museum of Earth Sciences - Cambridge

Department of Earth Sciences - University of Cambridge

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