Altar stone (Stonehenge)
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The Altar Stone is a central megalith at Stonehenge in England, dating to Stonehenge phase 3i, around 2600 BC. It is made of a purplish-green micaceous sandstone and is thought to have originated from outcrops of the Senni formation of the Old Red Sandstone in Wales, though this is currently in debate.[1] It was most recently excavated in the 1950s, but no written records of the excavation survive. It weighs six tons and would have stood nearly two metres tall. It is sometimes classed as a bluestone, because it does not have a local provenance. Now recumbent, it is thought to have originally stood as a single large monolith.