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]
