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Boulders at Moeraki.
They are spectacular examples of concretions, which form when a mineral precipitates from the ground water cementing the loose grains of sediment into solid rock. As you walk down the steep bluff to the beach you can see other enormous boulders being exposed as the ocean erodes the loose embankment. They eventually fall out of the embankment onto the beach.
The boulders are all large balls and a fascinating tourist attraction about 70 km north of Dunedin. Original public domain image from Flickr
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