Moeraki Boulders

Moeraki Boulders, New Zealand

There are a couple of places in this world, I really would like to see. A friend just added the Moeraki Boulders to this list, posting it to facebook.

These are spherical boulders off the coast of New Zealand of unusual size.

Moeraki Boulders

Moeraki Boulders

My first guess, would be dinosaur eggs (wouldn’t that be cool?). The actual explanation is almost as cool.

Before these boulders formed, they were just plain old mudstone. Then calcite came into the formation and functioned as cement. This isn’t unusual per se, but usually looks more like these caves in Romania.

La Zaplaz, Piatra Craiului

La Zaplaz, Piatra Craiului CC-BY-SA Amorphisman – Wikimedia

These limestone caves were formed by flowing of a calcite solution into the sediment. These caves are then usually formed by erosion.

So what’s so special about the Moeraki Boulders?

The calcites in the Moraeki formation diffused into the boulders, instead of a flow. Diffusion of this calcite solution into the mudstone caused a spherical spread of the calcites. The calcites then formed a cement in the mudstone. Later the ocean eroded the mudstone around these boulders to exhume them.

Addtionally, the boulders are riddled with septarian veins. They are harder veins from the inside out. Spetarians are still a geologic mystery. They thin out outwards and within the Moeraki boulders change throughout different stages from an outer brown calcite to an inner yellow calcite spar. Some rare boulder contain septarians that are partly covered in dolomite or quartz.

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... is a geophysicist by heart. He works at the intersection of machine learning and geoscience. He is the founder of The Way of the Geophysicist and a deep learning enthusiast. Writing mostly about computational geoscience and interesting bits and pieces relevant to post-grad life.

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