Some shock wave researchers have long contended that phase transitions of minerals under shock compression occur more rapidly than under comparable static compression conditions. Other researchers argue that phase transition behavior under shock compression does not differ from observations of static high pressure behavior. Many meteorites contain high‐pressure phases that are ascribed to impact. These high‐pressure phases are found within or adjacent to so‐called melt veins, sheets of material that was once molten and was quenched via conduction to surrounding material. Possible mechanisms for melt vein formation on impact include adiabatic shear and jetting. Thermal analysis of melt vein solidification and cooling, together with knowledge of phase stability fields and conditions for metastable survival of high‐pressure phases, constrains the shock conditions and provides evidence that the observed reconstructive phase transitions occurred via the same nucleation and growth mechanisms observed in static high pressure studies. © 2004 American Institute of Physics