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5
Igneous Rocks
The Organ Pipes in the Gawler Ranges are an example of columnar jointing, a geological structure where fractures in the rock form columns. Columnar jointing occurs in many types of igneous rocks and forms as the rock cools and contracts. These rhyolite pillars were formed 1500 million years ago when volcanic eruptions produced approximately 30 000km³ of lava. The temperatures reached were exceptionally high causing a highly viscous magma.
