Rocks, usually granite, which have abnormally high heat production as a result of the decay of radiogenic elements rather than merely residual heat. Potentially these are a source of geothermal energy. One method of exploiting the heat generated is to fracture the rocks at depth using small, down-hole, explosive charges, and then initiate a water circulation system from the surface. When cold water is pumped down it returns considerably warmer, and this energy can be extracted by heat exchangers. See also geothermal field; and geothermal gradient.
Subjects: Earth Sciences and Geography.