Relationships between radiation damage and trace water
in zircon, quartz, and topaz
Roger D. Aines and George R.
Rossman
Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, CA 91125, USA
Abstract
The presence of trace amounts of water or hyroxide ion can dramatically affect the
response of a mineral to radiation from both internal and external sources. In zircon, where
radioactive decay of U causes structural damage (metamictization), water can enter the
structure after a threshold of damage is reached and stabilize the metamict state by annealing
local charge imbalance. Quartz crystals with both amethyst and citrine zones have molecular
water in the citrine zones and dominantly hydroxide ion in the amethyst zones. This may
be due to the reduction of the amethyst Fe(IV) color center by atomic H formed by radiolysis
of the water. lntopaz, special hydroxide sites correlate with the formation of a brown color
center. The crystallographically identified hydroxyl on the (OH,D site does not appear to
be correlated with radiation damage. The mobility of H and the ease with which H-O
species may be formed in silicates appear to explain much of the role of hydrous species
in radiation-damage processes in minerals. These species occur in several charge states and
may anneal local charge imbalance. The occurrence of trace amounts of water in even
nominally anhydrous minerals makes this interaction common.