LIBYAN DESERT GLASS HOME
LDG
Libyan Desert Glass (LDG) is almost pure silica. It occurs in pieces weighing up to 16 lbs in the Sand Sea of the Libyan desert, in an area roughly 130 by 53 kilometers.

LDG

The enigma of this glass is:
1. The amount. It is the largest known deposit of a natural silica glass, ~98% SiO2 , on Earth.

2. It's distribution. The distribution is approximately elliptical, ~130 km by ~50 km with the major axis ~NNW by SSE.

3. Physical properties. The composition and structure of the glass are consistent with a hypothesis that the glass was formed from melted desert dune sand and subsequently cooled over a period greater than 24 hours in an Earth atmosphere.

4. Fusion energy. Possibly a meteorite or comet impact, but there are no meteor craters detectable from satellite photos with a resolution of ~5m within 150 km. No Libyan Desert Glass has been found at the nearest meteorite crater, located in Libya, ~150km to the west.

5. Chemistry. The glass cannot have been fused from the local exposed sandstone.

6. Age of glass and dunes. The dune sand and dunes have been formed in a time estimated to be less than 1,000,000 years, yet the fission track dates of the glass have a mean of ~28,000,000 years.

7. Surface geology. 28,000,000 years ago some geologists estimate that the sandstone was beneath ~300m of limestone and covered with vegetation.
[From: http://www.physics.wustl.edu/motd/DCOL00/1018.html]

LINKS:

The Stone of Tutanchamun

Libyan Desert Glass expedition

Libyan Desert Glass (Google)