Sarsen stones are sandstone blocks found in quantity in the United Kingdom on Salisbury Plain, the Marlborough Downs, in Kent, and in smaller quantities in Berkshire, Essex, Oxfordshire, Dorset and Hampshire. They are the post-glacial remains of a cap of Cenozoic silcrete that once covered much of southern England – a dense, hard rock created from sand bound by a silica cement, making it a kind of silicified sandstone. This is thought to have formed during Neogene to Quaternary weathering by the silicification of Upper Paleocene Lambeth Group sediments, resulting from acid leaching. The word "sarsen" (pronunciation ['sa:sǝn]) is a shortening of "Saracen stone" which arose in the Wiltshire dialect. "Saracen" was a common name for Muslims, and came by extension to be used for anything regarded as non-Christian, whether Muslim, pagan Celtic, or other. 
Fire and in later times explosives were sometimes employed to break the stone into pieces of a suitable size for use in construction. Sarsen is not an ideal building material, however. William Stukeley wrote that sarsen is "always moist and dewy in winter which proves damp and unwholesome, and rots the furniture". In the case of Avebury, the investors who backed a scheme to recycle the stone were bankrupted when the houses they built proved to be unsaleable and also prone to burning down. However, despite these problems, sarsen remained highly prized for its durability, being a favoured material for steps and kerb stones.
- Sarsen stones in Winchester at the City of Winchester website
- Stewart Ullyot, J.; Nash D.J.; Whiteman C.A.; Mortimore R.N. (2004). "Distribution, petrology and mode of development of silcretes (sarsens and puddingstones) on the eastern South Downs, UK". Earth Surface Processes and Landforms. 29 (12). Bibcode:2004ESPL...29.1509U. doi:10.1002/esp.1136.
- Stevens, Frank. "Stonehenge". www.sarsen.org. Retrieved 4 September 2014.
- Bruce Bedlam The stones of Stonehenge
- Stone ring of Avebury at Places of Peace and Power website