Scientists have identified Brazil’s first known field of tektites, glassy fragments produced when an asteroid struck Earth approximately 6.3 million years ago. The discovery, published in the journal Geology, adds a sixth entry to a very short list of major tektite fields identified worldwide.
The specimens have been named geraisites, after Minas Gerais, the Brazilian state where they were first found. The research was led by Álvaro Penteado Crósta, a geologist and senior professor at the Institute of Geosciences at the State University of Campinas (IG-UNICAMP), with collaborators from Brazil, Europe, the Middle East, and Australia.
A Strewn Field Spanning 900 Kilometers
The geraisites were first documented across three municipalities in northern Minas Gerais: Taiobeiras, Curral de Dentro, and São João do Paraíso, covering an area roughly 90 kilometers long. After the study was submitted, additional finds emerged in Bahia and later in Piauí, extending the total known distribution to more than 900 kilometers.
“This growth in the area of occurrence is entirely consistent with what is observed in other tektite fields around the world. The size of the field depends directly on the energy of the impact, among other factors,” Crósta said.
By July 2025, researchers had collected around 500 individual pieces. With subsequent discoveries, that total now exceeds 600. The fragments range from under 1 gram to 85.4 grams and measure up to 5 centimeters along their longest dimension. Their shapes, including spheres, ellipsoids, droplets, disks, dumbbells, and twisted forms, match the aerodynamic profiles typical of tektites, which are shaped by rapid flight through the atmosphere after an impact.
What the Fragments Look Like
The geraisites appear black and opaque under ordinary conditions. Held under strong light, they become translucent, revealing a grayish green hue. That coloring sets them apart from European moldavites, the bright green tektites from Central Europe that have been used in jewelry since the Middle Ages.
Their surfaces are marked by small pits. Crósta describes these as “traces of gas bubbles that escaped during the rapid cooling of the molten material as it traveled through the atmosphere, a process also observed in volcanic lava but especially characteristic of tektites.”
Chemical Analysis Confirms the Origin
Laboratory work confirmed the impact origin of the material. The geraisites contain high levels of silica (SiO2), ranging from 70.3% to 73.7%. Sodium oxide (Na2O) and potassium oxide (K2O) together account for 5.86% to 8.01%, slightly elevated compared to other known tektite regions. Trace elements including chromium at 10 to 48 parts per million and nickel at 9 to 63 ppm vary across samples, suggesting the target rock was not geologically uniform.
Researchers also detected rare inclusions of lechatelierite, a high-temperature glassy silica that only forms under extreme heat, adding further weight to the impact classification. Very low water content, measured by infrared spectroscopy, provided another decisive indicator.
The Crater Has Not Been Found
Before this discovery, five major tektite fields were known globally, located in Australasia, Central Europe, the Ivory Coast, North America, and Belize. The Brazilian field now joins that group, even though the source crater has not yet been located. Finding the impact structure will likely be the next significant challenge for researchers working on this discovery.
The find fills a notable gap in South America’s record of ancient impact events, a record that has historically been sparse compared to other continents.
Photo by NASA Hubble Space Telescope on Unsplash
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