Large, spherical Moeraki Boulders, Otago coast, South Pacific Ocean, South Island, New Zealand

South Pacific Ocean waves released the spherical Moeraki Boulders onto Koekohe Beach, between Moeraki and Hampden on the Otago coast, South Island, New Zealand. These ancient concretions grew 2 meters (6 feet) in diameter over 4 to 5.5 million years from marine mud (Moeraki Formation mudstone) near the surface of the Paleocene sea floor. After the concretions formed, large cracks (septaria) formed and filled with brown calcite, yellow calcite, and small amounts of dolomite and quartz when a drop in sea level allowed fresh groundwater to flow through the enclosing mudstone.

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Contained in galleries: NEW ZEALAND: Catlins, SE coast South Island

South Pacific Ocean waves released the spherical Moeraki Boulders onto Koekohe Beach, between Moeraki and Hampden on the Otago coast, South Island, New Zealand. These ancient concretions grew 2 meters (6 feet) in diameter over 4 to 5.5 million years from marine mud (Moeraki Formation mudstone) near the surface of the Paleocene sea floor. After the concretions formed, large cracks (septaria) formed and filled with brown calcite, yellow calcite, and small amounts of dolomite and quartz when a drop in sea level allowed fresh groundwater to flow through the enclosing mudstone.