| The rock cycle |
| Extrusive igneous rocks |
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These are probably basalts, but this cannot be determined with certainty from only a photo. þorlákshöfn, Iceland; 27 July 2014. |
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When lava cools rapidly, cracks at an angle of ca. 120° release most energy. As a result, hexagonal columns as seen here can be observed in many places. Svartifoss, Iceland; 20 July 2014. |
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Mont Gerbier de Jonc (Ardèche), France; 28 July 2011. A lava dome, formed by highly viscuous lavas that hardly flow. |
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| Huge solidified lava walls, south of Borgarbyggð, Iceland; 24 July 2014. |
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These collumnar basalts are on the mid-oceanic ridge, where the North American plate and the Eurasian plate spread apart. þingvellir, Iceland; 17 & 21 July 2014. |