Researchers have identified a new field of impact glass in northeastern Brazil, adding a sixth known tektite strewn field to the geological record. The discovery, published in December 2025 in the peer-reviewed journal Geology, describes roughly 500 specimens collected across an area at least 90 kilometers wide in the state of Minas Gerais.
The study was led by Álvaro Penteado Crósta, a geologist and senior professor at the Institute of Geosciences at the State University of Campinas. Radioactive argon isotope dating places the original impact at approximately 6.3 million years ago, during the late Miocene epoch.
What tektites are and why they rarely form
Tektites are natural glass objects created when a meteorite, comet, or asteroid strikes Earth with enough force to melt surface rock, launching superheated material through the atmosphere before it cools and solidifies. The word derives from Ancient Greek roots meaning “melted” or “molten.”
Before this discovery, tektites were confirmed to exist in only five distinct strewn fields worldwide, including the Australasian field, which covers roughly 10% of Earth’s surface, as well as fields in the Ivory Coast, the Czech Republic, and North America.
Their rarity comes down to two main factors. Rock composition matters: tektites tend to form from quartz-rich soils and rocks. Size of the impactor matters too. As researchers at the Jackson School of Geosciences at the University of Texas have noted, only large meteorites carry enough energy to melt rock and scatter molten debris across the distances required to form a strewn field.
The geraisites up close
The newly named “geraisites” follow the convention of naming tektites after their place of origin, similar to moldavites from the Czech Republic. The specimens range from 1 gram to 86 grams in mass and take various shapes, including spherical and drop forms.
They appear black and opaque under normal light. Exposed to intense light, they shift to a gray-green, translucent appearance. Their surfaces carry small cavities, remnants of gas bubbles that formed as the molten material tore through the atmosphere before cooling.
No crater yet
One significant gap remains: the source crater has not been located. Finding it would require identifying a geological structure capable of producing an impact event large enough to scatter 500 specimens across a 90-kilometer strewn field 6.3 million years ago.
Strewn fields can appear on land or settle into deep-sea sediments as microtektites, which complicates the search. The source impact site for other known fields has also proven elusive in some cases, making the Brazilian crater’s absence notable but not unusual within impact geology.
The geraisites now represent the first confirmed tektite strewn field in South America, a finding that expands both the geographic and geological map of where large impact events have shaped the planet’s surface.
Photo by Cédric Dhaenens on Unsplash
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