Using extremely high-resolution microscopy, Reto Gieré, professor and chair of the Department of Earth and Environmental Science in Penn’s School of Arts & Sciences, and his coauthors found that not only had the lightning melted the rock’s surface, resulting in a distinctive black “glaze,” but had transferred enough pressure to deform a thin layer of quartz crystals beneath the surface, resulting in distinct atomic-level structures called shock lamellae.
http://www.upenn.edu/pennnews/news/lightning-reshapes-rocks-atomic-level-penn-study-finds