Glass, as we know it, is manufactured for us. It is made by melting sand, lime, and soda in blast furnaces, at very high temperature. When the mixture is liquid, impurities are removed; the resulting product is glass, which is allowed to cool until it is ready for blowing or molding into useful shapes.
It is interesting to know that, in addition to the manufactured product, there is a kind of glass made by nature. It doesn't come in sheets, like window panes, or in any other form that can be used commercially, but chunks of it can sometimes be found in sandy places.
Specimens of natural glass, called fulgurites, are made as a result of lightning striking dry sand. Sometimes, when the electrical current of lightning passes through sand, materials in the sand are fused together by the heat of the lightning so that strips of glass are formed. When this glass cools, it hardens and may be picked up, although it is quite brittle and must be handled very carefully.
It takes over three thousand volts of electricity to fuse sand into a fulgurite. Lightning is much more powerful than this and so it is quite possible for glass to result from the heat of lightning acting on sand.
When fulgurites are found, they are usually rough on their outer surface, and have a hollow tube going through the center.
These strange glass oddities are frequently pearl-gray in color, but they have also been known to be yellowish, reddish, green or brown. Some very rare fulgurites have been black. The color of a fulgurite is determined by minerals in the soil where it was fused. For instance, carbon causes a black color, but iron will produce various shades of reddish brown.
Some places where fulgurite deposits have been found are the Alps, the Pyrenees, the Rocky Mountains, Great Lakes region and the Atlantic coast. Where one fulgurite is found, there are usually more. This is due to the fact that some types of sand are more easily fused than others.
The reason for the appearance of fulgurites in mountain areas is the presence there of sandstone and mineral compounds that contains sand.
Large fulgurites, since they are so brittle, are impossible to get out of the ground in one piece.
It takes experience and a sharp eye to discover a fulgurite even on the surface, and not all of them are on the surface. They have been known to be as far as forty feet underground.