The so called Libyan Desert Glass is the purest natural silica glass ever found on earth. The glass is generally yellow in color. It can be very clear or it can be a milky, and even contain tiny bubbles, white wisps, and inky black swirls.
Over a thousand tons of these glass are strewn across hundreds of kilometers of bleak desert. Most of these are the size of pebbles polished smooth by the abrasive action of the blowing sand. Others are chunks of considerable size and weight. The biggest piece ever found weighed around 26 kg.!
Natural glass, such as Libyan Desert Glass, can be formed either by lightning strike, or volcanic activity or meteorites striking the earth.
The Libyan desert glass has been dated as having formed about 26 million years ago, which made scientists assume that the glass here was formed when a meteorite struck earth around this time, but the absence of an impact crater pose problems for this theory. In 2007, a circular feature was discovered using satellite images but evidence of it being an impact crater is slim to none.
Another theory suggest an exploding comet near the surface heating up the sand beneath it to a extreme temperatures resulting in the formation of a huge amount of silica glass.