English: Libyan Desert Glass from the Oligocene of Egypt. (4.0 centimeters across at its widest)

Large & small impacts have affected Earth since its formation 4.55 billion years ago. Compared with the intensely pitted and cratered Moon, Earth has relatively few preserved impact craters, because they have been destroyed by water & glacial erosion. Impact events are accompanied by tremendous amounts of heat, resulting in melting of much of the ejected pulverized bedrock at ground zero. The melted material cools quickly, and falls back to Earth in the form of impact splash glasses (a.k.a. tektites). Tektites are principally composed of amorphous silica (SiO2). Broken surfaces show a conchoidal fracture. Tektites from different impact events are given different names.

Tektites called Libyan Desert Glasses are known from a large area in western Egypt’s Libyan Desert. These nearly pure silica glasses range in color from pale yellowish to yellowish-green to brownish. Their surfaces have been sculpted by wind-blown sand abrasion. Available age information indicates that these rocks formed during the mid-Oligocene (28.5 million years ago). The responsible impact crater(s) have not been identified with certainty.