A tektite is a natural glass formed when a meteorite slams into Earth with enough force to melt the rock and soil at the impact site, launching molten material high into the atmosphere. Unlike meteorites, which come from space, tektites are made entirely of terrestrial material that was superheated, ejected, and cooled into glass during its flight. They range from tiny beads smaller than a millimeter to chunks weighing over 20 kilograms, and they’ve been found on every continent except Antarctica.
How Tektites Form
When a meteorite strikes Earth at hypervelocity (typically 15 to 70 kilometers per second), the shock energy generates temperatures far above the melting point of the surrounding rock. This creates a pool of impact melt as the transient crater blows open. Only about 1 to 3 percent of that melt gets ejected at extremely high speeds, sometimes faster than the meteorite itself. This small, superheated fraction is what becomes tektites.
The ejection happens in the very earliest moments of crater formation. A plume of molten and vaporized rock jets outward under enormous pressure, pushing the atmosphere aside and allowing the molten droplets to follow long ballistic trajectories across hundreds or thousands of kilometers. As the vapor expands and cools, it breaks the melt into small droplets. Those droplets then collide and merge into larger bodies of glass. During this process, virtually all water, organic carbon, and carbon dioxide is stripped from the original rock, which is why tektites end up being among the driest natural materials on Earth, with water content as low as 0.008 percent by weight.
What Tektites Are Made Of
Because tektites form from melted surface rock and sediment rather than volcanic magma, their chemistry reflects whatever was on the ground at the impact site. They’re rich in silica, the same compound that makes up quartz and most sand. Their silica content is generally high, and some varieties contain minerals like coesite, a form of silica that only forms under extreme pressure, providing direct evidence of a violent impact origin.
The extreme heat involved in their formation burns off nearly all volatile compounds. This makes tektites dramatically drier than volcanic glasses like obsidian, which typically contain around 0.1 to 0.3 percent water. Tektites hold roughly 10 to 30 times less. Certain metallic elements, particularly iron, nickel, cobalt, and chromium, are also partially lost during formation because they form volatile compounds at extreme temperatures.
Shapes and Why They Vary
Tektites come in three broad categories, and the shape tells you something about how far they traveled from the crater.
- Muong Nong-type tektites are the largest, with specimens reported up to 24 kilograms. They have a blocky, layered appearance with visible internal structure and tiny gas bubbles. These land closest to the impact site because they follow shorter, lower trajectories.
- Splash-form tektites are the classic shapes most people picture: spheres, teardrops, dumbbells, and elongated droplets. These solidified from spinning, stretching blobs of melt during flight and landed at intermediate distances from the crater.
- Aerodynamically shaped tektites include buttons, flanged buttons, and lens shapes. These traveled the farthest, re-entering the atmosphere at high speed after being lofted on long ballistic arcs. The distinctive flanges and flow ridges on their surfaces formed when the glass partially re-melted from aerodynamic heating during re-entry, much like a spacecraft’s heat shield.
NASA laboratory experiments have confirmed this re-entry explanation. By subjecting glass to hypervelocity ablation conditions, researchers reproduced the exact ring-wave ridges, coiled flanges, and subsurface flow patterns seen on Australian tektites. About 98 percent of Australian tektites show aerodynamically stable shapes consistent with atmospheric re-entry ablation.
The Five Known Strewn Fields
Tektites aren’t scattered randomly across the globe. They cluster in distinct zones called strewn fields, each linked to a single impact event. Five are currently recognized.
The North American strewn field is the oldest at roughly 35 million years. It produced tektites known as bediasites (found in Texas) and georgiaites (found in Georgia), and its source is the Chesapeake Bay impact crater, whose inner basin measures about 40 kilometers across.
The Central European strewn field, about 14 million years old, produced the green, translucent tektites called moldavites. These originated from the Ries crater in southern Germany, a 24-kilometer-wide impact structure that’s now a well-studied geological landmark.
The Ivory Coast strewn field dates to roughly 1 million years ago. Its tektites trace back to the Bosumtwi crater in Ghana, a 10-kilometer-wide depression now filled by a lake.
The Australasian strewn field, at about 780,000 years old, is by far the largest. It stretches from Southeast Asia across the Indian Ocean to Australia, covering roughly a tenth of Earth’s surface. Despite its enormous size, the source crater has never been definitively identified. A 2020 study published in the Proceedings of the National Academy of Sciences proposed a location beneath a volcanic field in Laos, but the question remains one of geology’s more intriguing open puzzles.
A fifth, more recently recognized Central American strewn field dates to about 800,000 years ago, nearly the same age as the Australasian field, though its relationship to other strewn fields is still being studied.
How to Tell Tektites Apart From Other Rocks
Tektites are sometimes confused with obsidian or other volcanic glass, but several features set them apart. Their extremely low water content is the most definitive chemical difference. Structurally, many tektites show flow lines, stretched bubbles, and surface textures (called sculpturing) created by chemical etching in acidic soil over thousands of years. Splash-form tektites in particular have smooth, rounded shapes that look nothing like the sharp, conchoidal fractures typical of obsidian.
Color varies by strewn field. Moldavites are typically olive green to forest green and translucent enough to be used in jewelry. Australasian and Ivory Coast tektites tend to be dark brown to black and opaque. North American bediasites are usually dark olive to black. In all cases, tektites feel surprisingly light for their size due to their glassy, low-density composition.
Why Tektites Matter to Science
Tektites serve as physical evidence of past asteroid impacts, some of which are otherwise difficult to study because the craters have eroded, been buried, or lie underwater. Their chemical signatures act as fingerprints that can be matched to specific impact sites, helping geologists identify and date ancient collisions. The Australasian strewn field, where the crater itself hasn’t been confirmed, is a case where the tektites are actually better preserved than the impact structure that created them.
Their aerodynamic shapes also made them valuable to early space-age researchers. Because tektites experience genuine atmospheric re-entry heating, studying their ablation patterns helped NASA engineers understand how materials behave during high-speed descent, contributing to heat shield design for spacecraft in the 1960s.