In her Bright Star project, Anne Dunn is working on molecular dynamic simulations of quartz breakage, resulting from an applied shear stress, in an aqueous environment. Water molecules affect the Si-O bonds at the outer quartz surface, through solvation, and along the fracture surface (possible cleavage surface) as the fracture propagates through the quartz structure, the process known as stress corrosion.
Most of us were taught in introductory geology that one of the integral properties of quartz is conchoidal fracture (and the absence of cleavage). It turns out that this is not exactly true. Rapid breakage does result in conchoidal fracture, but quartz can exhibit cleavage and it is not uncommon in samples found in certain types of geologic environments.
It has been hypothesized that slow fracture propagation in the presence of an aqueous fluid, through the process of stress corrosion, may lead to the development of quartz cleavage planes. This video, courtesy of Alan Hart, shows a particularly striking example. This is a quartz crystal that grew from a hydrothermal fluid into an open space in a vein (in Hot Springs, Arkansas). During the growth process the crystal was cleaved and the two pieces were displaced but not separated. Continuation of quartz precipitation along the cleavage plane “healed” or recombined the two pieces into what is now a single crystal again.