We got an early start so we could stop to see the Moeraki boulders at low tide. These huge spherical stones are scattered like billiard balls along the beach. These are no ordinary rocks, they’re septarian concretions (rocks formed in unique geologic settings that contain mineral crystals in the interior of the structure). They formed in the ancient seafloor sediment, sort of like the way oyster pearls are formed – layers of material cover a nucleus/core. Lime minerals form around an irritant like a fossil shell, bone fragment or wood piece and over time the seabed has lifted up and exposed these 3 ton boulders. The ones with deep ridges or veins show more erosion. Pretty amazing, huh?