Features, Geology Talk

Concretions: Inexplicable spherical rocks


Though concretions are almost perfectly smooth and round, these rock formations are in fact completely naturally occurring.

The manufactured-looking round balls of rock, have washed up on a variety of different locations throughout the years, on the shoreline of Canada to the shores of New Zealand.

The strange concretion phenomenon is common but takes millions of years to form. The concretions are a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces commonly found in sedimentary rock.

Concretions are found across areas of Kodiak Island on Alaska’s southern coast and Qeqertarsuaq in Greenland.

Geologists have also observed a link between concretions and the preservation of fossils, with the rounded rocks having found to frequently contain well-preserved fossils.

One theory is that the presence of dead animals or plants may contribute to the formation of the concretions, through the element of calcium cementing smaller sedimentary particles together.

Another theory is that the concretions simply have a better environment and structural makeup to preserve fossils than other surround rocks.

According to Geologist Survey of Canada researcher Marc St-Onge, the strange rock formations are formed when a pile of sediment made from mud, silt or sand is located near a flowing body of water.

Other harder materials found in bodies of water, such as shells, leaves and fossils, are then pushed into the sediment pile through the flowing water, providing the calcifying element for the formation of the concretion.

The spheres are formed when that ‘cementing mineral’ dissolves in the sediment pile, such as calcite, which forms limestone within the concretion.

For millennia, layers of concrete-like rock form on top of the pile – with the outer layers being softer and easier to erode.

Not all of the concretions are perfectly spherical, as some that are only close to a decade old are more similar to ovals in shape.

To form a perfect sphere, Onge estimated it takes millions of years from the impacts of waves and ice.

Additionally, the growth of the concretions, despite the constant erosion that results in the spherical shape, persists only until there is no more calcium present in the sediment of the running water. Due to this, larger concretions are more commonly found in areas of high mineral sediment concentration.

Whilst a mystery in the true secrets of their creation, as to truly observe the formation of naturally occurring concretion, much longer studies must be conducted, the concretions are perfectly natural, despite their commonly perfectly spherical appearance.

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