Thursday, November 20, 2014

Moeraki Boulders - Crystalline Eggs Hatch Beautiful Birds?

Giant eggs that hatch fabulous women? Gourds or eel baskets washed from an ancient canoe of the gods? Marbles lost by some young giant?

The truth is even more interesting. The Moeraki Boulders--located 40 kilometers south of Oamaru on New Zealand's Otago coast--are calcite-cemented "septarian concretions" exposed through weathering of the surrounding, softer mudstone in low cliffs behind the beach, then concentrated by wave action. They are one of the top free natural landmarks in New Zealand.

Nearly perfectly spherical, the boulders originally formed much like a pearl, through the slow replacement or cementing of mudstone by calcite, concentrically outwards from a nucleus over millions of years. Now the boulders are up to 3 meters in diameter and can weigh several tonnes. The softer interiors of the boulders are typically hollow and/or lined with crystals, from which extend outwardly-radiating, calcite-filled cracks called septaria. These give the boulders an almost "Humpty Dumpty" appearance of a reassembled egg.

A close-up of some weathered boulders highlighting the calcite septaria.

No kids, these are too big for dinosaur eggs.

The Moeraki Boulders are located on Koekohe Beach, midway between Hampden and Moeraki townships in North Otago. Access is via small spur (Moeraki Boulders Road) with parking and beach access, 1 mile north along Hampden-Palmerston Road (SH 1) from Hillgrove railway platform.