Scientists in Brazil have uncovered evidence of a previously unknown impact event recorded in hundreds of glassy fragments scattered across the country.

Scientists have confirmed the first known field of tektites ever discovered in Brazil. Tektites are pieces of natural glass created when an extraterrestrial object strikes Earth with tremendous force, melting surface rock and ejecting it through the atmosphere. The newly identified specimens have been named geraisites after the state of Minas Gerais, where they were first found. Their discovery adds an important new chapter to South America’s still-limited record of ancient impact events.

The findings were detailed in the journal Geology by a research team led by Álvaro Penteado Crósta, a geologist and senior professor at the Institute of Geosciences at the State University of Campinas (IG-UNICAMP). The project included collaborators from Brazil, Europe, the Middle East, and Australia.

Before this discovery, scientists recognized only five major tektite fields worldwide, located in Australasia, Central Europe, the Ivory Coast, North America, and Belize. The Brazilian strewn field now becomes part of this small and scientifically significant group.

Researchers first identified geraisites in three municipalities in northern Minas Gerais, Taiobeiras, Curral de Dentro, and São João do Paraíso, across an area roughly 90 kilometers long. After the study was submitted for publication, additional samples were documented in the neighboring states of Bahia and, more recently, Piauí. According to Crósta, the known distribution now stretches 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,” he explains.

By July 2025, researchers had collected about 500 specimens. Continued fieldwork has increased that total to more than 600. The pieces vary considerably in size, weighing less than 1 gram at the smallest and up to 85.4 grams at the largest. Some measure as much as 5 centimeters along their longest dimension. Their forms reflect the aerodynamic shaping that occurs while molten material travels through the atmosphere, producing spherical, ellipsoidal, drop-shaped, discoid, dumbbell-shaped, and twisted varieties.

Physical and Optical Characteristics

At first glance, the fragments look black and opaque. When exposed to strong light, however, they become translucent and reveal a grayish green tone. This appearance differs from European moldavites, which have been used in jewelry since the Middle Ages because of their vivid green color. The outer surfaces of the geraisites are dark and pitted with numerous small cavities.“These small cavities are 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,” says Crósta.Chemical testing further supports their impact origin. Analyses show that the geraisites are rich in silica (SiO₂), with concentrations ranging from 70.3% to 73.7%. The combined levels of sodium (Na₂O) and potassium (K₂O) oxides fall between 5.86% and 8.01%, slightly higher than those measured in other tektite fields. Researchers also detected variations in trace elements, including chromium (10-48 parts per million) and nickel (9-63 ppm), suggesting that the source rock was chemically diverse rather than uniform. Rare inclusions of lechatelierite, a high-temperature glassy form of silica, provide additional evidence of extreme heating during formation.

“One of the decisive criteria for classifying the material as a tektite was its very low water content, as measured by infrared spectroscopy: between 71 and 107 ppm. For comparison, volcanic glasses, such as obsidian, usually contain from 700 ppm to 2% water, whereas tektites are notoriously much drier,” Crósta points out.

Dating the Impact Event

Dating based on the ratio of argon isotopes (⁴⁰Ar/³⁹Ar) indicates that the event occurred approximately 6.3 million years ago, at the end of the Miocene epoch. Three groups of very similar ages were obtained (6.78 ± 0.02 Ma, 6.40 ± 0.02 Ma, and 6.33 ± 0.02 Ma), which is consistent with a single impact event. “The age of 6.3 million years should be interpreted as a maximum age since some of the argon may have been inherited from the ancient rocks targeted by the impact,” the researcher comments.

To date, no associated crater has been identified. According to Crósta, this is not unusual; only three of the six large classical tektite fields have known craters. In the case of the largest field, located in Australasia, the crater is believed to be oceanic. In Brazil, isotopic geochemistry indicates that the molten material originated in Archean continental crust between 3.0 and 3.3 billion years old. This directs the search to the São Francisco craton, an ancient and geologically stable portion of the continental crust and one of the oldest regions of the South American continent.

“The isotopic signature indicates a very ancient continental, granitic source rock. This greatly reduces the universe of candidate areas,” says Crósta. In the future, aerogeophysical methods such as magnetic and gravimetric surveys may reveal circular anomalies associated with a buried or eroded crater.

Modeling the Impact and Broader Implications

While it is not yet possible to accurately estimate the size of the impacting body, researchers consider it unlikely that it was small. The large amount of molten material and the wide area of dispersion indicate a significant impact event, albeit smaller than the event responsible for the Australasia field, which extends for thousands of kilometers.

The team is currently working on a mathematical model of impacts to estimate parameters such as the energy released, the velocity, the angle of entry, and the volume of molten rock. They are doing this as new data on the spatial distribution of geraisites becomes available. The discovery of the geraisites fills an important gap in the record of impacts in South America. Only about nine large impact structures are known there, and almost all of them are much older and located in Brazil. This discovery also reinforces the idea that tektites may be more common than previously thought, but often go unnoticed or are mistaken for ordinary glass.

To combat sensationalist interpretations of cosmic impacts, Crósta manages the @defesaplanetaria Instagram profile with undergraduate students. The profile is dedicated to scientific dissemination and differentiating real risks from irresponsible speculation about meteorites and asteroids.

Impacts were frequent during the formation of the solar system when a large amount of debris was scattered, and planetary orbits were undefined. Large bodies migrated from one position to another, projecting smaller bodies in various directions. However, today, with the system stabilized, impacts are incomparably less frequent. “Understanding these processes is essential to separating science from speculation,” the researcher concludes.