About 20 million years ago, the Sahara Desert melted. The immense heat formed Libyan Desert Glass, which covered hundreds of square miles.
Libyan Desert Glass’ value comes from the miraculousness of its origin story. As Dr. Jane Cook, chief scientist at The Corning Museum of Glass in Corning, New York, explains, “glass happens when just the right ingredients are heated up and cooled down quickly.” But in the case of Libyan Desert Glass, the series of events was much more elaborate. “About 20 million years ago, either a meteor impact or atmospheric explosion got to the desert part of the lower atmosphere, heated it up and fragmented and exploded,” she says. “It dumped a huge amount of heat, like in thousands of Fahrenheit degrees, into that portion of the desert, which was a relatively pure deposit of quartz sand. And it brought it up hot enough that it was able to liquefy for a short period of time.” When this liquefied quartz cooled down, desert glass was formed. Cook adds: “Because it was almost pure silica it was able to solidify without crystallizing,” making it glass instead of geological crystal structures.
Any millions years later, when humans discovered the glass, it was considered as precious stone, and it even ended up in King Tut's tomb. Read about Libyan Desert Glass at Atlas Obscura.