One of the pebbles at Moeraki, North Otago....also known as the Moeraki Boulders. Moeraki village is in the background.
"Scientists explain the boulders as calcite concretions formed about 65 million years ago. Crystallization of calcium and carbonates around charged particles gradually formed the boulders in a pearl-like process that took as long as four million years. The soft mudstone containing the boulders was raised from the seabed around 15 million years ago; waves, wind and rain are excavating them one by one."
There are about 60 boulders left on the beach and the largest are 2 to 3 metres in diameter and weigh about 7 tons. Many were taken from the beach but have been protected for decades. They were perfectly spherical but erosion is getting to them as will be seen in further photos.