Geraisite

Geraisites are newly confirmed tektites from Brazil. They were named after the state of Minas Gerais, where the first specimens were found. Their scientific description was published in 2025, and they represent the first confirmed occurrence of a tektite strewn field in Brazil.

Geraisites formed approximately 6.3 million years ago during a major impact event. When a cosmic body struck the Earth, terrestrial rocks were exposed to extreme temperatures, melted, and part of the resulting melt was ejected into the atmosphere. During flight, the material cooled rapidly and solidified into natural glass – tektites.

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The First Confirmed Tektites from Brazil

The first specimens were found in the northern part of the Brazilian state of Minas Gerais. The currently documented strewn field extends for at least approximately 90 kilometres and includes the area between the municipalities of São João do Paraíso and Curral de Dentro. Since research began, hundreds of specimens of various sizes and shapes have been found.

Appearance of Geraisites

Geraisites are predominantly black to dark brown and have a strongly pitted surface. When viewed in transmitted light, some specimens may show olive-brown to greenish shades. They occur in various forms, including spherical, ellipsoidal, teardrop-shaped, disc-shaped and dumbbell-shaped forms, which developed as the molten material travelled through the atmosphere.

Chemical Composition and Age

In terms of chemical composition, geraisites correspond to natural silicate glasses and display properties typical of tektites. The water content of the analysed specimens is exceptionally low, approximately 70–110 ppm. Current ⁴⁰Ar/³⁹Ar dating places their age at approximately 6.3 million years.

Source Crater

Although the impact origin of geraisites is well established, the source crater has not yet been identified. Their discovery therefore provides important evidence of a previously unknown major impact event in South America and significantly expands the known global distribution of tektites.