Certain materials immersed in liquid fluorine or fluorine-containing liquid propellants explode or ignite when subjected to impact or shock loading. The pressure waves resulting from such loading may cause microstructural changes in the interior of materials. Under shock loading, tantalum, columbium, and titanium alloys exhibit discoloration on the specimen surface and dislocation cell structures within crystalline grains throughout the specimen. The commercial polytetrafluorethylene often causes explosive reactions. The shock waves propagating through the specimen cause pronounced microstructural changes by the formation of microvoids and spherulites. Electron microscopic studies reveal that these spherulites consist of regular arrays of thin (200 to 300 A thick) blade-like lamellae containing 20 A wide segments. These presumably are helices of fluorocarbon molecular chains formed similarly to Hoffman's model of chain folding and extended chain crystallization.