Elvan is a name used in Cornwall

Cornwall

Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...

 and Devon

Devon

Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...

 for the native varieties of quartz-porphyry

Quartz-porphyry

Quartz-porphyry, in petrology, is the name given to a group of hemi-crystalline acid rocks containing porphyritic crystals of quartz in a fine-grained matrix, usually of micro-crystalline or felsitic structure...

. They are dispersed irregularly in the Upper Devonian series of rocks and some of them make very fine building stones (e.g. Pentewan stone, Polyphant stone and Catacleuse stone). Greenstone is another name for this stone and it is often used for parts of buildings such as doorways so they can be finely carved. Most of the elvan quarries are now disused. Others are quarried in bulk for aggregates commonly used for road-building.