Figure 7
From: The response of zircon to the extreme pressures and temperatures of a lightning strike
Stability fields for polymorphs of zircon dissociation products, SiO2 and ZrO2 (modified after ref.2, which built on diagrams of, most notably, refs.10,11,38,43). Polymorphs of SiO2 are shown with thin lines and coloured fields and polymorphs of ZrO2 are shown with thicker lines and annotated fields. Bdy baddeleyite, c cubic, o orthorhombic, t tetragonal. Dashed lines and question marks reflect (1) uncertainty in the up-temperature continuation of the zircon dissociation reaction line due to unknown effects of liquid silica on phase stability2, and (2) uncertainty in the temperatures at which cubic ZrO2 melts at high pressures38. Red shading indicates the likely formation conditions of cubic ZrO2 in the York County fulgurite given estimated pressures of up to a few GPa (see text).
