On the surface of the sand free corridors among the great dunes of the southern part of the Great Sand Sea lie one of the most enigmatic mysteries of the Libyan Desert - chunks of green through yellow to white Libyan Desert Glass (LDG), a mineral made up of almost 100% pure silica in an amorphous, glassy state.

The mineral was first encountered by Patrick Clayton at the end of December, 1932. In 1934 Clayton Dr. L.J. Spencer of the Natural History Museum undertook an expedition to study this strange mineral, and the debate on the nature and formation of this strange substance continues to this date. One thing is certain: LDG can only be found in a large ovel area, approximately 40 (N-S) by 20 (E-W) kilometres at the southern tip of the Sand Sea to the north of the Gilf Kebir, and nowhere else.

     

LDG has been compared to other naturally occurring glasses of volcanic and impact origin, and two alternate theories exist to explain it's formation. The hot formation theory (apparently prefereed by the majority of researchers) suggests that the glass was formed during a high energy impact of a comet fragment or other extraterrestrial object. The cold formation theory suggests that the glass was the product of hydrothermal activity. Both theories leave questions unanswered, and both explain features that the other seemingly cannot. There is convincing research suggesting that the glass was formed at temperatures higher than any hidrothermal activity could have produced, however the lack of any convincing impact structures in the vicinity questions the impact origin. Also the hot formation theory cannot explain the clearly banded structure and dark organic intrusions observed in some pieces, which points to an origin in a super-saturated aquatic solution. There is no clear winner, just a large number of open questions. The best source for the state of the art theories is a special issue of the Sahara Journal, containing the proceedings of the 1996 "Silica" conference held in Bologna.

The area near the tip of one of the dune ranges within the LDG area was a fairly large lake during the neolithic pluvial. The pink mud filling the lake basin is clearly recognisable, and the surrounding area is particularly rich in prehistoric remains, including numerous microliths formed from LDG.