"Buried mineral gains such as quartz absorb and store energy from natural background radiation. The longer the grain is buried, the more the stored energy. When a buried grain is exposed to light, this energy is released as light; when the grain is reburied, the energy again begins to accumulate. Measurement of the amount of energy and of the rate of radiation on the burial environment are the basis for OSL dating (optically-stimulated luminescence) - the quarts grains acting as a resettable crystal timer... Quartz grains are common and very resistant to decay; where conditions are favourable, OSL can provide dates back to around half a million years ago - well beyond the reach of radio carbon, and a critical period for human evolution."*

Could be useful in dating rock art and 'newer' worked areas on monoliths.

* To see lost worlds in grains of sand by Sebastian Payne. British Archaeology Magazine. September-October 2006, page 54.