What are the large spherical boulders on Koekohe Beach in New Zealand called?

The large spherical boulders on Koekohe Beach in New Zealand are called the Moeraki Boulders. They lie along the Otago coast between the settlements of Moeraki and Hampden and are among New Zealand's most recognizable natural attractions.

Despite their almost artificial appearance, the boulders are geological formations known as septarian concretions. They formed within layers of mudstone over millions of years as minerals accumulated around a central nucleus. Cracks later developed inside them and were filled with minerals, creating the distinctive patterns seen on broken surfaces.

Coastal erosion gradually stripped away the softer mudstone surrounding the concretions. Waves and weather then exposed and concentrated the giant spheres on the beach. Some are more than two metres across, and many appear in clusters or partly buried in the sand.

The boulders are sometimes confused with hoodoos or balanced rocks, but those terms describe different erosion shapes. Giant's Causeway is also unrelated: it consists of polygonal basalt columns in Northern Ireland, not spherical concretions in New Zealand.