Self-induced fracture generation in zircon

Zircon has particular geological significance because of its use in the age determination of rocks and as a structural analogue phase for radioactive waste forms. However, radiation damage of the crystal structure (metamictization) causes a volume expansion of the crystal lattice and the generation of internal stresses which can induce fractures in the crystal. A model has been developed which predicts that spatially distinct radial and/or concentric fracture sets can be produced, and such fracture patterns accurately describe the distribution and types of self-induced fractures observed in natural zircons. In general, the formation of such microfractures in zircon is a function of the degree of metamictization, shell thickness, and the confining pressure. Results suggest that the types of fractures found in a suite of zircons from a particular rock might be potential indicators of the depth of burial. Because metamictization-induced fractures may serve as potential pathways for the rapid leaching of various elements from the zircon crystal, this may also have important implications in interpreting the U/Pb ages of fractured zircons or in evaluating the suitability of related crystalline phases as hosts for nuclear waste. -from Authors