The mysterious Libyan desert glass.

As found in one of the most remote areas of the Sahara

In 1996 in the Egyptian Museum in Cairo, Italian mineralogist Vincenzo de Michele spotted an unusual yellow-green gem in the middle of one of Tutankhamun's necklaces. 

The jewel was tested and found to be glass, but intriguingly it is older than the earliest Egyptian civilisation. 

Working with Egyptian geologist Aly Barakat, they traced its origins to unexplained chunks of glass found scattered in the sand in a remote region of the Sahara Desert.

The central scarab in King Tut's breast plate is made of this glass.

The glass has generated intense interest among scientists because its origin remains an enigma. Was it produced by the encounter of an extraterrestrial body with earth? Science isn't sure and, in fact, has come up with at least 10 theories to explain its origin.

Many researchers consider Libyan Desert glass to be a form of tektite (from the Greek tektos, meaning molten), a natural black, dark green, or dark brown glassy stone, resembling the volcanic glass obsidian, that may possibly be of extraterrestrial or meteoritic origin. Tektites, which occur in four large associations of distinctly different ages throughout the world known as strewn fields, are similar to Libyan Desert glass in that both substances are composed chiefly of silica (silicon dioxide); the silica content of tektites ranges from 68-80 percent whereas that of Libyan Desert glass is approximately 98 percent. Both tektites and Libyan Desert glass are characterized by etched, pitted surfaces, which in the case of some of the silica glass may have been obscured by the scouring action of the fierce Saharan winds.  But is Libyan Desert glass a tektite? 

Although it usually is discussed in the same context as tektites and is considered by some investigators to be a variety of tektite, there exist some very distinct differences. Libyan Desert glass has a uniformly higher silica content than tektites, and it shows no evidence of aerodynamic sculpturing. Many of the fragments are tabular and layered, which is characteristic of only one kind of tektite, the so-called Muong-Nong tektites of southeast Asia. Libyan Desert glass never occurs in such distinctive shapes as dumbbells, rods, spheres, disks, and teardrops as do tektites, and the color of the glass is rarely as dark as the color of typical tektites. In fact, some of the glass is quite colorless. It ranges in size from tiny flakes 0.01mm in diameter up to pieces the size of a person's head and weighing over 16 pounds. Both tektites and Libyan Desert glass are harder than the steel in a knife blade, but no harder than the mineral quartz. Fragments of Libyan Desert glass are somewhat lighter weight than tektites of equal size. Both tektites and Libyan Desert glass may contain bubbles.

Analyses of both major and trace elements of the glass and of the Nubian Sandstone upon which it rests, together with the stratification visible in numerous pieces, have revealed that the Nubian Sandstone is a suitable parent material for Libyan Desert glass and suggest that the glass could be of impact origin. What is not yet understood is the mechanism that produced, momentarily, heat intense enough to melt surface rock or weathered debris. For the quartz-rich Nubian Sandstone, the melting temperature would be about 2,800°F.

Virgil Barnes has suggested that perhaps the glass was produced by the heat wave of a passing comet or by the intense heat generated by an exploding comet - neither of which would necessarily disrupt the surface rocks. Afterwards, the molten silica glass may have flowed into low areas, puddled and cooled - thus forming Libyan Desert glass. Later, it may have been broken up by weathering and then moved, either by running water, in an earlier, wetter climatic period, or by humans in prehistoric times.