Tektites are unique, natural glass objects formed as a byproduct of massive cosmic impacts on Earth’s surface. They are not meteorites, but terrestrial rock that has been melted, ejected into the atmosphere, and rapidly cooled into a glassy state. Identifying a true tektite requires careful examination of its physical traits, which are a direct result of this extreme formation process.
Formation and Strewn Fields
Tektites originate from the hypervelocity impact of a large meteorite on the Earth’s surface. The immense energy of the collision instantly melts the local soil and rock, ejecting this molten material high into the atmosphere. This material then cools and solidifies into glass droplets before falling back to Earth, often hundreds or thousands of kilometers from the impact site. The resulting glass is characterized by an extremely low water content, typically less than 0.02% by weight, which distinguishes it from volcanic glasses like obsidian.
The distribution of these glassy bodies is restricted to specific, geographically extensive areas known as strewn fields. There are four major, globally recognized strewn fields: the Australasian, North American, Ivory Coast, and Central European. Tektites found within a single strewn field share similar chemical compositions and ages. This consistency helps scientists link them back to a single impact event, even if the source crater remains undiscovered, as is the case with the Australasian field.
Visual Identification: Primary Physical Markers
The visual identification of a tektite begins with recognizing its characteristic, often aerodynamic shape. As the molten material flies through the air, surface tension and rotation shape it into “splash forms” like spheres, teardrops, dumbbells, discs, and rods. Some tektites, notably those from the Australasian field, exhibit secondary features like flanges and button shapes, which result from partial re-melting and ablation during high-speed re-entry into the lower atmosphere.
The color is most commonly black or dark brown, although regional varieties exist, such as the translucent green Moldavites from the Central European field and the yellowish-green Libyan Desert Glass. Regardless of color, the surface displays a vitreous, or glassy, luster when freshly fractured. The defining external trait is the surface texture, often referred to as “sculpting,” which includes distinctive pitting, grooves, and flow lines.
This unique sculpting is caused by the high-speed passage through the atmosphere and subsequent chemical etching in the ground over millennia. The glass itself is amorphous, meaning it lacks a crystalline structure. Internally, tektites may contain small, nearly spherical or elongated gas bubbles, also known as vesicles, which were trapped during the rapid cooling phase. They also possess lechatelierite, a form of pure silica glass created by the intense heat of the impact, which is a key diagnostic feature.
Confirmation Steps and Distinguishing Look-Alikes
To move beyond visual cues, several physical tests can help confirm a tektite identification and differentiate it from common mimics. Tektites have a Mohs hardness ranging from 5.5 to 6.5, roughly the hardness of window glass. Another characteristic is specific gravity, or density, which typically falls between 2.3 and 2.5, placing them in a range denser than some natural glasses but lighter than many crystalline rocks.
A simple, non-destructive test involves checking for magnetism, as tektites are non-magnetic. This helps rule out industrial slag, which frequently contains trapped metal fragments and is often magnetic. Slag often displays unnatural colors, excessive bubbles, and a different internal structure compared to the homogeneous composition of a tektite.
The most common natural look-alike is obsidian, a volcanic glass that shares the same amorphous, silica-rich nature. The primary differentiator is the water content: tektites are nearly anhydrous, while obsidian contains a significant amount of trapped water. Obsidian typically shows flow banding and may contain fine mineral specks, features absent in true tektites. The characteristic surface pockmarks of a tektite are also distinct from the smoother or irregularly fractured surface of obsidian.