For the first time, researchers have identified a field of tektites in Brazil, marking a significant addition to the global record of extraterrestrial impacts. These natural glasses, formed by the high-energy collision of celestial bodies with Earth’s surface, have been named “geraisites” after the Brazilian state of Minas Gerais, where they were first discovered. This discovery not only expands the incomplete record of impacts in South America but also adds Brazil to the list of regions with recognized tektite fields.
The groundbreaking discovery was detailed in an article published in the journal Geology, led by Álvaro Penteado Crósta, a geologist and senior professor at the Institute of Geosciences at the State University of Campinas (IG-UNICAMP). Crósta collaborated with a diverse team of researchers from Brazil, Europe, the Middle East, and Australia to unveil this new strewn field.
Joining the Elite Group of Tektite Fields
Until now, only five large tektite fields were recognized globally: Australasia, Central Europe, the Ivory Coast, North America, and Belize. The Brazilian field now joins this exclusive group, highlighting its scientific significance. Initially located in three municipalities in northern Minas Gerais—Taiobeiras, Curral de Dentro, and São João do Paraíso—the field spans approximately 90 kilometers. Recent findings have extended its reach to the Brazilian states of Bahia and Piauí, increasing its known area to over 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,” explains Crósta.
Characteristics and Composition of Geraisites
By July 2025, researchers had collected around 500 specimens, a number that has since grown to over 600. These fragments vary in size from less than 1 gram to 85.4 grams, with the longest axis reaching about 5 centimeters. The geraisites exhibit typical aerodynamic shapes such as spherical, ellipsoidal, drop-shaped, discoid, dumbbell-shaped, or twisted.
Although they appear black and opaque initially, geraisites become translucent under intense light, revealing a grayish-green hue distinct from the intense green of European moldavites, which have been used in jewelry since the Middle Ages. Their dark surfaces are marked by many small cavities, indicative of gas bubbles escaping during rapid cooling.
Geochemical analyses reveal that geraisites have a high silica (SiO₂) content ranging from 70.3% to 73.7%, with sodium (Na₂O) and potassium (K₂O) oxides ranging from 5.86% to 8.01%, slightly higher than other tektite fields. Trace elements such as chromium and nickel were also identified, suggesting non-homogeneous original material. The presence of rare lechatelierite inclusions further supports an impact origin.
Unraveling the Impact’s History
Dating based on the ratio of argon isotopes (⁴⁰Ar/³⁹Ar) indicates the impact event occurred approximately 6.3 million years ago, at the end of the Miocene epoch. Consistent age groups suggest a single impact event, though no associated crater has been identified yet.
“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,” Crósta comments.
Isotopic geochemistry points to an origin in the Archean continental crust, directing the search for a potential crater to the São Francisco craton, one of the oldest regions of the South American continent. Future aerogeophysical methods may reveal circular anomalies associated with a buried or eroded crater.
Implications and Future Research
While the size of the impacting body remains uncertain, researchers consider it unlikely to have been small, given the large amount of molten material and wide dispersion area. The team is developing a mathematical model to estimate impact parameters such as energy released, velocity, angle of entry, and volume of molten rock.
The discovery of geraisites fills a crucial gap in South America’s impact record, where only about nine large impact structures are known, most of which are much older and located in Brazil. This finding also suggests that tektites may be more common than previously thought, often overlooked or mistaken for ordinary glass.
To address sensationalist interpretations of cosmic impacts, Crósta manages the @defesaplanetaria Instagram profile with undergraduate students, focusing on scientific dissemination and differentiating real risks from irresponsible speculation about meteorites and asteroids.
“Understanding these processes is essential to separating science from speculation,” Crósta concludes.
About São Paulo Research Foundation (FAPESP)
The São Paulo Research Foundation (FAPESP) is a public institution dedicated to supporting scientific research across all fields by awarding scholarships, fellowships, and grants to investigators linked with higher education and research institutions in São Paulo, Brazil. FAPESP collaborates internationally, encouraging scientists funded by its grants to further develop their research through global partnerships. Learn more at www.fapesp.br/en and stay updated with FAPESP’s latest scientific breakthroughs at www.agencia.fapesp.br/en.
