Tektites are small, glassy objects formed from terrestrial material subjected to extreme heat. They are typically black, brown, or dark green, and their presence has long been a source of scientific mystery. Tektites are confined to specific geographic areas, and their unique composition offers a glimpse into violent cosmic events that have shaped Earth’s history.
Definition and Key Characteristics
Tektites are natural glasses, lacking the crystalline structure of minerals. They are highly siliceous (over 65% silica) and characterized by extremely low water content (less than 0.02% by weight). This composition distinguishes them from terrestrial volcanic glass, such as obsidian, which contains significantly more trapped water.
Their color ranges from opaque black or dark brown to translucent olive or yellowish-green. Internally, they contain lechatelierite, a pure silica glass formed under extreme heat and pressure. Tektites exhibit various external forms, including spheres, teardrops, dumbbells, and disks, known as splash forms. These shapes often have unique surface textures like pits, grooves, and flow lines, resulting from their rapid formation and travel through the atmosphere.
Formation Through Hypervelocity Impact
Tektite formation results from the melting and ejection of surface rock caused by a hypervelocity meteorite impact. When a large object collides with Earth, kinetic energy converts instantly into heat and shock waves, vaporizing and melting the local terrestrial rock and soil.
The molten terrestrial material is ejected at high velocity, sometimes escaping the atmosphere and traveling thousands of kilometers away. As these droplets fly through the atmosphere or space, they cool rapidly, solidifying into glass before falling back to Earth. This rapid cooling prevents the formation of microscopic crystals (microlites) found in slower-cooling volcanic glasses.
During re-entry, the high-speed descent causes aerodynamic ablation—a secondary melting and shaping of the solidified glass. This creates distinct forms, such as the button-shaped tektites found in Australia, characterized by a flange around the rim. The composition is overwhelmingly terrestrial; they are transformed Earth rock, not material from the impacting space object. Specific isotopes confirm the parent material was silica-rich surface sediment or crustal rock.
Global Distribution and Classification
Tektites are concentrated within geographically limited areas known as strewn fields. Each field is linked to a single, powerful impact event. Scientists recognize four primary strewn fields, each named for its general geographical location.
The largest and youngest is the Australasian strewn field, covering over 10% of the Earth’s surface, spanning Southeast Asia to Australia (790,000 years old). This field includes types such as Australites and Indochinites. The Central European strewn field (14.8 million years ago) is the source of Moldavites, notable for their translucent green color and etched surfaces.
The North American strewn field is the oldest (35 million years), including Bediasites from Texas and Georgiaites from Georgia. The Ivory Coast strewn field in West Africa is the smallest (1.07 million years old). Tektites are classified by the strewn field where they are found, linking them to a specific impact event and composition.
Scientific Importance and Collecting Value
Tektites provide unique samples of Earth’s upper crustal material subjected to extreme heat and pressure. Their distinct chemical signatures and precise ages, determined through radiometric dating, allow researchers to accurately date major impact events. Tektites have helped locate or confirm associated impact craters for three of the four known strewn fields, such as the Ries crater in Germany and the Chesapeake Bay impact structure in the United States.
The study of tektites and microtektites (smaller than one millimeter) helps map the extent of ancient impacts and their effect on the global environment. Analyzing their properties provides crucial data for understanding the mechanics of hypervelocity collisions. Beyond science, tektites are highly valued by collectors and frequently used in jewelry. The translucent green Moldavite is sought after for its vibrant color and intricate sculpting, making it a commercially valued impact glass.