How we know that this is a piece of fossilized lightning

Lightning struck the Sahara desert about 15,000 years ago, and left a sign of its presence behind. The heat from the lightning reached a little over 1,800C and melted certain elements in the soil until they fused together. This solid form, called a fulgurite, most often shows up in sandy soil, or soil with a lot of… » 2/28/13 12:40pm 2/28/13 12:40pm