The Great Sand Sea of the eastern Sahara is aptly named; an unbroken mass of dunes the size of New Mexico which smothers the barren frontiers of Libya and Egypt and is home to not one living soul. Parallel dune ridges run north-south for hundreds of miles, and anyone journeying here has to be exceptionally well prepared, as there's not a single well or water source in 150,000 square miles--extreme even by Saharan standards.
Until the 1930s, this hyper-arid region had barely been explored, but during WWII, clandestine German and British desert patrols, including Count Almasy, aka The English Patient, probed this remote area, spying on each other's movements. Today, the area still remains largely unknown and is so rarely visited that 60-year-old tire tracks are still visible on certain surfaces.
The Great Sand Sea is a peculiar place. Being the world's third largest dune-field, the Egyptian Sand Sea is a desert in its own right. It spans 650 km between Siwa in the north and the Gilf Kebir plateau in the south. It's average width of 300 km spans from the Libyan border to the west and the Farafra Depression to the east. Totaling the size of England, the sand accumulation varies in shape, color and geologic origin from one place to the other.
On the southern shore of the Sand Sea--on the Egyptian side close to the Libyan border and a hundred miles from the nearest tree lies a unique geological oddity: the world's only known field of silica glass, tiny pebbles of pale green glass, their upper surface polished by the incessant winds. There are also chunks weighing up to ten pounds, half buried like icebergs in the reddish sand. But the finest specimens are the tiny pebbles lying windblown on the desert floor, scoured by millennia of sand storms into lustrous prisms of glass.
The exact origin of the glass is still unknown. A plausible theory suggests that the sand, which is almost pure silica, was fused by the intenseheat of a meteor impact. But no crater,
let alone a partially fused or aerated piece, has ever been found. Which suggests a less exciting origin: a super-saturated lake of silica that slowly dried into pure natural glass hard enough to resist a scalpel's mark.
On the eastern edge lies the Nummulite Scarp and the sole water source of Ain Dalla. The southern region of the Great Sand Sea is a mysterious place dotted with legends of lost oases (Zarzora), disappearing armies and secret caravan routes.