Scientists have identified mysterious bluish-green materials recovered from an ancient archaeological site in northwestern Argentina, revealing that many were not made of the mineral previously believed. Laboratory tests revealed that several green fragments from Rincón Chico were atacamite, rather than malachite, while other finds included turquoise and silica-rich minerals.
Researchers used X-ray diffraction, or XRD, to determine the composition of selected specimens. The analysis showed that materials with similar green or blue-green appearances could have very different mineral compositions.
Green minerals were not what they seemed
Archaeologists have historically used the term “malachite” to describe many green copper-bearing materials found in the region. The new analysis found a different mineral was common among the tested specimens.
XRD identified atacamite as the predominant mineral among several samples from Rincón Chico. The results suggest that some material previously described as malachite at the site may also have been atacamite.
Scientists encountered another surprise when they analyzed specimens selected because they looked like copper minerals. Some were actually silica-rich materials containing minerals such as quartz and opal. The findings show that color alone cannot reliably establish the composition of archaeological minerals.
Identifying atacamite also raises questions about where the material came from. The mineral commonly forms in extremely dry environments and is abundant in northern Chile. Its presence in northwestern Argentina has therefore sometimes been linked to long-distance exchange. However, atacamite also occurs naturally in Catamarca, Salta and La Rioja.
Discovery raises questions about ancient trade
Researchers said the available evidence cannot determine whether the Rincón Chico atacamite came from nearby deposits or farther away.
Small-scale copper mining has been documented in the southern Yocavil Valley. At the same time, minerals moved considerable distances across the Andes before European contact. Evidence from ancient copper bells discovered in Bolivia has also pointed to long-distance exchange networks across the southern Andes.
Scientists have identified mysterious green minerals found at an ancient site in Argentina. Tests revealed atacamite, turquoise and evidence that metalworking and ornament production took place side by side at Rincón Chico. pic.twitter.com/RXgRtJttUD
— Tom Marvolo Riddle (@tom_riddle2025) August 31, 2026
Turquoise recovered at Rincón Chico presents a similar problem. Important turquoise sources existed in Chile, but the mineral also occurs in parts of Argentina.
Researchers identified three turquoise beads at Rincón Chico 15 along with other turquoise pieces. One fragment showed smoothing and more regular edges, suggesting possible human modification.
The concentration of beads and related fragments raises the possibility that people worked turquoise at the site rather than simply bringing in finished ornaments. Other archaeological evidence from Bolivia has revealed connections stretching from the Andean highlands to the Atacama Desert and Pacific coast.
Finds point to more than metalworking
Shell objects strengthen the evidence for ornament production. Researchers identified 11 specimens made from the land snail genus Megalobulimus, including finished beads and an unfinished piece. They also found a fragment of freshwater mussel shell that may have been intended as raw material.
The discoveries are significant because Rincón Chico 15 has long been associated with metallurgy. The combination of turquoise, shell beads, copper minerals, and other materials suggests craftspeople carried out several kinds of production in the same area.
Researchers also identified an aragonite flake and other colored mineral fragments. Some pieces showed possible signs of working, although the study said the evidence was not strong enough to establish human modification in every case.
Archaeological discoveries of ancient copper workshops elsewhere have similarly helped researchers reconstruct how ancient communities processed mineral resources.
Color may have influenced ancient choices
The findings raise another possibility: Ancient people may sometimes have selected minerals because of how they looked, not simply because of their chemical composition.
Green and blue materials could differ substantially at the mineral level while sharing striking visual qualities. Color, brightness, and the ability to shape a material may therefore have influenced which pieces people collected and used.
Across the southern Andes, green and blue minerals have been found in ornaments, metalworking, and ritual settings. However, the researchers cautioned that the presence of a green mineral does not prove that it held a particular cultural meaning or served a specific purpose.
The new analysis instead shows that Rincón Chico’s seemingly similar green materials represented several different minerals and potentially several different uses.
Further geological and chemical analysis will be needed to establish where the atacamite and turquoise originated. Researchers also hope that non-destructive techniques can identify tiny fragments that cannot undergo conventional XRD analysis without being damaged.
The findings reshape the picture of Rincón Chico. Its mysterious green materials were not a single resource used for one purpose. They included different minerals connected to metalworking, ornament production, and a wider system of material selection in the ancient southern Andes.
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