  Although quartz ($\rm \alpha$-form) is a mineral used in numerous
applications wherein radiation exposure is an issue, the nature of the
atomistic defects formed during radiation-induced damage have not been fully
clarified. Especially, the extent of oxygen vacancy formation is still debated,
which is an issue of primary importance as optical techniques based on charged
oxygen vacancies have been utilized to assess the level of radiation damage in
quartz. In this paper, molecular dynamics (MD) simulations are applied to study
the effects of ballistic impacts on the atomic network of quartz. We show that
the defects that are formed mainly consist of over-coordinated Si and O, as
well as Si--O connectivity defects, e.g., small Si--O rings and edge-sharing Si
tetrahedra. Oxygen vacancies, on the contrary, are found in relatively low
abundance, suggesting that characterizations based on $E^{\prime}$ centers do
not adequately capture radiation-induced structural damage in quartz. Finally,
we evaluate the dependence on the incident energy, of the amount of each type
of the point defects formed, and quantify unambiguously the threshold
displacement energies for both O and Si atoms. These results provide a
comprehensive basis to assess the nature and extent of radiation damage in
quartz.

Materials Science;Nuclear Theory