Moeraki Boulders

Notable for their near-perfect spherical shape and abundance in a dramatic setting, the iconic Moeraki Boulders of the Hampden area of coastal North Otago are probably the best known, most photographed and talked about concretions in New Zealand. These have formed in mudstones of the Moeraki Formation that are  Paleocene age (~55-60 million years old), and are eroding out of the cliffs to become exposed on the shoreline.
 Detailed studies (see Boles et al 1985) have revealed that in composition, these concretions show a calcium enrichment- magnesium depletion with growth by diffusion (from core to edge). Larger boulders at Moeraki may have taken some 4 million years to form, however new studies being undertaken by a Japanese team suggest formation may have been much quicker! (see Yoshida et al. 2018).
*More images coming soon!

Septarian veination with crystals of calcite

Moeraki Boulders in Maori mythology:

After an epic voyage across the Pacific, the great Maori migration waka (canoe) Arai-te-Uru finally overturned at Matakaea (Shag Point), where the cargo of eel pots, gourds, and kumera were turned to stone - forming the curious spherical and ovoid boulders seen along the coast.