For some reason the natural glass in the Great Sand Sea of Egypt is always referred to as silica glass which is odd as all glass is made of silica unless it's plastic…..anyway this natural glass is 98% silica which makes it the purest natural glass in the world. Other glasses, such as volcanic obsidians are lower in silica at 75%.
The natural glass of the Sand Sea is found in a large area stretching from just north of the Gilf Kebir to a few hundred km south of Siwa. The area of highest concentration is small but I’ve found small pieces of glass spread over a long but not wide distance. Mainly the glass is confined to four dune corridors - the ones used by cars storming up from the Gilf to Siwa.
The glass was formed by a giant meteorite hitting the earth it is widely believed. Dated as being formed 29 million years ago when there was 1000 extra feet of earth/rock covering the earth’s surface; which is why we can’t see the meteorite spot - apparently - though Farouk Al Baz has found a 32 km diameter meteorite spot some hundred km or so south of the main area. This could work - though I doubt if even a comet would blow a hole a 1000 foot deep.
That the glass was formed from a space object is confirmed more or less by the presence of large quantities of iridium and more than a terrestial quota of nickel and other minerals. A massive explosion and impact is needed to make clear glass - if you look at artificial impactites formed by H and A bomb desert tests they look like fulgarite - that nobbly hollow bubbly glassy stuff caused by lightning strikes in sand. To make big lumps of pure glass you’d need the power of many thousands of H bombs in one spot.
Other mysteries about the sand sea glass: it has no bits of rock adhering - these pure lumps are not found in other tektite sites in Moldovia and Saudi Arabia. The largest lump found was 57lbs and is in a French Natural History museum. A 10kg lump found by Pat Clayton is in the Cairo Geological Museum - always worth a visit in its dusty shack-like quarters along the Corniche just before Maadi. I’ve found some 1kg lumps and if you look hard you may too.
Someone calculated from the spread of glass that 14 million tons of the stuff would have been generated. You get the feeling that it rises up through the sand over time. Other nice finds include worked pieces of glass - anything from 20,000 to 3,000 years old – as Australian Aborigines switched to glass from broken bottles direct from worked stone, it’s hard not to imagine ancient man using glass if he had the chance.
The glass was first mentioned in modern times by traveller Fulgence Fresnel in 1846, though Tutankhamun’s pectoral scarab has been shown to be carved from the stuff, and not from quartz as was thought previously. The scarab, of course, in Egyptian mythology rolls the sun across the sky, so a glass scarab that catches the light kind of fits. I once was given a piece by Rupert Harding Newman, the last member of the Zerzura club who died only recently. He had collected two big bags of the stuff back in 1935. “I don’t suppose there is any left now,” he said, a little shamefacedly.