Boulders of Taranaki

 

You’ve probably heard of the famous Moeraki Boulders, but have you heard of the Taranaki Boulders? The Taranaki coastline hides a secret: large boulders rivaling the famed Moeraki Boulders. These impressive geological formations can be found at various points along the coast, some still embedded within the sandstone cliffs.

The boulders are in fact concretions. Concretions develop through a process of mineral precipitation and cementation within sedimentary rocks or soil. They typically begin to form around a nucleus, which can be organic material like a shell or piece of bone, or inorganic matter such as a grain of sand. Over time, minerals dissolved in groundwater accumulate around this core, gradually building up layers that solidify into a compact, often spherical shape. The composition of concretions varies depending on the surrounding environment and available minerals, with common materials including calcite, siderite, or silica. This process can take thousands to millions of years, resulting in concretions that range from pebble-sized to massive formations several meters in diameter.