Sergio (carbonado)
The Sergio was the largest rough diamond ever dug up on earth. It was known to weigh. But see the update below in which the weight is revised to 3,245 carats. It was found above ground in Lençóis in 1895 by Sérgio Borges de Carvalho.
The Sergio was first sold for $16,000 and later for to Joalheria Kahn and Co. and shipped to G. Kahn in Paris, who sold it to I. K. Gulland of London in September 1895 for. It was then broken up into small pieces as industrial diamond drills.
The precise circumstances surrounding Sergio's discovery, his export to Paris, and then to London, have been rediscovered and extensively corrected .
Like other carbonados, the Sergio is believed to be of meteoritic origin. However, most recent publications have confirmed that this cosmological hypothesis is becoming less and less credible, as various teams have measured clearly terrestrial characteristics in various carbonados, including possible signatures isotopic of terrestrial biological origin.
Between 2023 and 2024, two historical casts of Sergio were found at the Natural History Museum in London, and an older one at the French National Museum of Natural History in Paris which cast had been made by the French chemist and Nobel Prize winner, Henri Moissan.
A photograph of Sergio before its destruction was even found at the French MNHN in 2025: it was originally published in 1913 in a book by J. Escard without its name ‘Sergio’, a name that was coined much later by the Gemological Institute of America around 1955. An image analysis using hierarchical clustering based on different linkage methods proves that the best-known photograph of this carbonado is probably the photograph taken around 1900 of a fourth moulding then kept at the Instituto Geográfico e Histórico da Bahia. This photograph shows an object that has all the characteristics of the cast found in Paris and donated by Moissan to the IGHB.
Finally, Sergio's weight was revised in 2025 because it was given in 1895 in old Brazilian carats and had not been converted to modern metric carats: thus, the published weight of 3,167 carats has been corrected to 3,245 modern metric carats, as confirmed by the analysis of the Paris cast at the MNHN as well as writings of Henri Moissan himself in 1895.
A fifth cast of the Sergio was 3D printed from polylactic acid and donated in 2025 by MNHN Prof. Francois Farges to the Sociedade União dos Mineiros in Lençóis, where it has been on display ever since.