Glass Formation

  • Glass, Glaciers, and the Geography of the Midwest

    lipari obsidienne 28529Glass is formed naturally under a number of circumstances. Rapidly cooling magma can produce obsidian, a black glassy rock with a high silica content similar to man-made glass. Glass is also formed when lightning strikes sand or soil causing the silica to melt. Some meteorite impacts even apply enough shock pressure to force silica in the ground into a glass.