Vugs are small cavities inside rock that are formed when crystals form inside a rock matrix and are later removed through erosive processes, leaving behind voids. A common cause of vugs is minerals precipitating from solution in water, and then later being dissolved again by less saturated water. The inner surfaces of vugs are often coated with some of the mineral matter that formed them. Fine crystals are often found in vugs where the open space allows the free development of external crystal form. Geodes are a common vug formed rock.

The word vug was introduced to the Engliah language by Cornish miners, from the days when Cornwall was a major supplier of tin.

Vug also refers to a Titanian individual in Philip K. Dick's science fiction novel The Game-Players of Titan, ISBN 0679740651.

VUG is also an acronym for Vivendi Universal Games.

"The Vug" is a popular website that provides links to all things Mineral related. ^* Petrology