No. 64: Jul-Aug 1989
Pieces of Libyan Desert Glass weighing as much as 16 pounds are found in an oval area measuring approximately 130 by 53 kilometers. The clear-to-yellowish-green pieces are concentrated in sand-free corridors between north-south dune ridges. The origin of this immense deposit of glass has been attributed by some to ancient nuclear explosions and alien activities, but investigating scientists have always been satisfied with a meteor-impact hypothesis. A recent study (abstract below) also opts for this explanation, although no one has found a crater of suitable size or other supporting evidence.
"Libyan Desert Glass (LDG) represents 1.4 x 109 g of natural glass fragments scattered over about 6500 km2 of the western Desert of Egypt. We made a systematic study (employing INAA, microprobe and mass spectrometry techniques) of several varieties of LDG and locally associated sand and sandstone to provide insight into the nature and formation of these enigmatic glass fragments. These studies indicate that:
- Although the LDG has restricted major element compositions (97.98 wt% SiO2 ; 1-2 wt % Al2 O3 ) their trace element contents (ppm) (Fe, 490-5200; Co, 0.2-1.2; Cr, 1.2-29 and Sc. 0.462.5) vary by as much as a factor of 5 to 30.
- The LDG fragments exhibit a factor of three variation in the REE abundances (La, 5.4-15.3 ppm). They all show parallel and steep LREE enriched patterns ([La/Sm]N , 3.8-4.2) and flat HREE ([Tb/Lu]N , 1.1- 1.2) and distinct negative europium anomalies (Eu/Eu*, about 0.5).
- The gases in the vesicles of LDG (N2 , Ar, O2 , CO2 , H2 O and their dissociation products) are present in proportions consistent with derivation from the terrestrial atmosphere.
- Dark streaks present in some samples of LDG contain significantly higher siderophile element abundances (Ir, about 0.5 ppb), possibly representing a meteoritic residue."Our studies suggest that LDG is the product of meteorite impact into quartz-rich surficial eolion and alluvial sand, and perhaps also into quartz-rich sandstone, of the western Desert of Egypt."
(Murall, A.V., et al; Eos, 70: 379, 1989.)
Reference. Libyan desert glass and other unusual natural glasses are cataloged in ESM2 in Neglected Geological Anomalies. To order this catalog, visit here.