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Chadwell St Mary Sarsen Stone, CHADWELL ST. MARY, Thurrock District, TQ64637850, General geological site
Site category: Boulders - sarsen Site name: Chadwell St Mary Sarsen Stone Grid reference: TQ 6463 7850 Brief description of site: In the churchyard of Chadwell St. Mary church is a sarsen stone (1 metre x 0.5 metres x 0.35 metres in size) with mammillated surfaces. ----------------------------------------------------------- Sarsen stones Sarsens are extremely hard boulders of sandstone formed around 55 million years ago when the climate of Britain was hot and a layer of sand on the surface of the Chalk became cemented with quartz. They are thus very resistant to erosion and have survived the rigours of the Ice Age. The formation of silcretes (which includes sarsens and puddingstones) has been the subject of recent scientific debate. Research has compared the conditions under which sarsens and puddingstones may have been formed with the present day climate in the Kalahari Desert and parts of Australia. The sarsen stones of Thurrock are some of the best-preserved examples in the UK and most have curious rounded protuberances on their surfaces (mammilated), which are growth structures formed as the quartz slowly crystallised between the sand grains.
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