In 1996, this piece on display at the Egyptian Museum of Cairo caught the eye of a mineralogist. As it turned out, the yellow-green gem in the middle of this pectoral of King Tutankhamun’s (1332–1323 BCE) was Libyan desert glass, a variety of tektite. Photo by RolandUnger. Licensed under CC By-SA 3.0. (Cropped to show detail).
Tektite is a natural glass formed from the ejected debris of meteorite impacts. Though most pieces are very small, some tektite varieties have been cut and used for jewelry since prehistoric times.
Tektites are popular as “raw stones” for jewelry or as display pieces. The value of these rough specimens depends greatly on their shape, size, and visual appeal.
Tektites large enough to be cut into gemstones are rare. The value of cut tektites depends mostly on their size, transparency, color, and cut quality. Most tektites are opaque and have dark colors. Thus, translucent and lighter gems tend to sell for higher prices. However, opaque and dark gemstones also have their aficionados.
Scientists have proposed different theories about the origins of tektites. For example, it has been argued that tektites formed from an explosive event on the Moon and were thrown all the way to the Earth’s surface. However, current scientific consensus holds that tektites formed from the impact of meteorites on the Earth’s surface. Material from the Earth, melted on impact, was ejected into the atmosphere, then fell back to the surface and cooled into tektites.
Unlike stony, iron, and stony-iron meteorites recovered on Earth, tektites have terrestrial origins. Although formed by meteorite impacts, the tektites themselves have never been in outer space. The composition of tektites is consistent with terrestrial materials.
Tektites may be confused with another variety of natural glass: obsidian. While tektite is rare, obsidian is very common, which may lead to some misidentifications. This volcanic rock has many properties that overlap with those of tektite: color, hardness, specific gravity, and RI.
This near total absence of water makes possible another, more dramatic, way to distinguish tektites from obsidians. Jim Tobin explains this procedure in his 2003 article on tektite testing. When gently heated with an oxy-acetylene flame, obsidians will froth and become pumice. In contrast, tektites won’t froth. However, after cooling down, they’ll invariably shatter within a few hours due to thermal stress. (Obviously, this test isn’t recommended for finished gems).
Lapidaries have faceted moldavite gems weighing up to 25 cts. Other, more rarely faceted tektites are typically much smaller, although large pieces of rough indochinite and Libyan desert glass have been found.
Tektites range in hardness from 5 to 6.5, which makes them susceptible to scratching. (Household dust, with a hardness of 7, would easily scratch their surfaces). As ring stones, they should receive protective settings and only occasional wear. However, other jewelry uses, such pendants and earrings, should present no problems.