The origin of the Dakhla Glass (DG) had puzzled scientists since MAXINE KLEINDIENST discovered it in 1987 nearby the Dakhla Oasis (Egypt).
Some researchers had suggested the "Stone Age" glass may have been produced by burning vegetation or lightning strikes.
But a chemical analysis showed that the glass was created in temperatures so high that they could only have been the result of an impact event.
Gordon Osinski, a geologist at the Canadian Space Agency in Saint-Hubert who conducted the analysis, found that the glass samples contain strands of molten quartz, a signature of meteorite impacts.

"The Dakhleh Glass-forming impact event occurred during the Middle Stone Age time of occupation, but the timing of this event has not been well established. 40Ar/39Ar incremental heating of three aliquots from a sample of Dakhleh Glass yield data that can be ascribed to quenched glass which efficiently purged radiogenic 40Ar inherited from the target rocks. One of the aliquots yielded data suggestive of an undegassed clast of target material, but these are easily resolved. The age of the impact event is determined from a compositionally filtered subset of the data that yield an isochron age of 145 � 19 ka."

Fragments of so-called Dakhla Glass appear in clumps of ancient lake sediment.
Photos by A. Haldemann / J.M. Kieniewicz

My belief is: The Dakhla "Glass" is not caused by an airburst or impact event

The Dakhla "Glass" is a glassy andesitic lava !

Apparently is the occurrence of "Dakhla Glass" associated with Middle Pleistocene lacustrine sediments in situ. But this can be a fallacy. It can be also moved material of older period, coming from distantly regions. A determination of the age of the material of ~150 ka is mysterious. It is assumed that this indicates the age of the sedimentary embedding and so the age of the Paleo-lake.

Dakhla glass is quite variable. Smaller pieces tend to be highly vesiculated while bigger lumps can be mostly crystalline and dense. The glass is chemically distinctive, being unusually rich in calcium and aluminum. It contains small enclaves of very high silica glass (lechatelierite) which forms at temperatures greater than 1700 degrees C. Interestingly, about one third of the pieces show imprints of plant matter on their surface, indicating that the original melt were still of sufficiently low viscosity. There is also sometimes seen a flow-stretching to the vesicles and a tendency for them to be present in greater abundance near the upper surface of a given specimen, again indicating fluid behavior that allowed the bubbles to stretch and rise. The plant residues must be from the Tertiary period. The striation on the surface point to a Phragmites (reed), which existed since the Tertiary period.. The plant residues are attached with the glassy mass and was transported together.

The Dakhla Glass (DG) was probably a volcanic glassy mass, mixed with gases.
The new investigations (Osinski et al, 2008) confirm for me, that the DG's are redeposited, therefore it is not in situ. The glasses have probable a Tertiary age. The volcanic origin of the glassy mass in the context with the spread subvolcanic activities in the southwestern region is probable. Hydrovolcanic events are to be found everywhere in the region, also in the White and Black Desert in the north (look here).

The Dakhla Glass (DG) is emerged at the same time like the Libyan Desert Glass. It consists mainly of gas-rich volcanic outflow mass, which are mixed with sediment. The Libyan Desert Glass (LDG) is probably orthomagmatic-hydrovolcanic of origin and have an age of ~28 Ma (Oligocene). Both glasses differ however by the chemistry and origin substantially (look here).

Between the Dakhla region and the Gilf Kebir plateau in the southwestern direction exists an immense amount of examples for subvolcanic activities in the Tertiary period (look here). This region is rich of craters, basaltic plugs and dykes, which contain fused sandstones and breccias as well as fractured quartz grains. The place of the source is to be found in this large crater field of the "Scarp-Contours" in the southwestern direction. The Dakhla Glass (lava) after transport and destruction was deposited in a new position. Now it is found allochthonous near Dakhla in younger paleo-lake sediments as lumps.

By Osinski et al. (2008) published chemical analyzes clearly documents an andesitic (dioritic) composition of the DG

The results of the analysis are therefore surprising, because obviously no exists a direct relationship to the basaltic effusions in the region of Gilf Kebir and elsewhere in Egypt. Therefore we can assume a special origin, similar to the origin of the LDG. In both cases, a reference to an impact or airburst event is absurd. Already the attempt fails, to find target sediments for such compositions. It is sure igneous material, what came along of deep faults in this volcanic active region in the Oligocene period, in which also hundreds of subvolcanic structures emerged.

"Dakhleh Glass was first observed during regional archaeological and palaeoenvironmental surveys in the 1980s and 1990s (Kleindienst et al. 2006), with 6 known occurrences (Osinski et al. 2007). In 2007, we carried out a systematic search and discovered DG at ~140 different locations throughout the Dakhleh Oasis.
Based on this new work, it is clear that DG occurs in 4 main settings: (1) as a lag deposit on the deflated surfaces of Pleistocene lacustrine CSS; (2) in situ within the same sediments as lag deposits on Taref Formation sandstone surfaces in close proximity to the Pleistocene lacustrine sediments, but in areas where these sediments have been completely removed, and (4) redeposited on, or into, Holocene pan sediments. Searches of both older Quaternary formations and younger alluvial terraces yielded no DG fragments. Thus, an important observation is that the DG glass appears to be spatially associated with Middle Pleistocene lacustrine sediments. Recent fieldwork shows that these sediments were deposited in a lake (s).