Finding fragile fragments of iron

Archaeologists have confirmed that the iron fragments unearthed from Sanxingdui, a renowned archaeological site in Guanghan, Sichuan province, are made of pure meteoritic iron — the earliest such discovery in Southwest China.

The study, conducted by Sichuan University's School of Archaeology and Museology in collaboration with the Sichuan Provincial Institute of Cultural Relics and Archaeology, was recently published in the international academic journal Archaeological Research in Asia.

The three iron fragments, dating back to the late Shang Dynasty (c. 16th century-11th century BC), can be pieced together into a complete axe-shaped artifact measuring about 20 centimeters long and five to eight cm wide.

Li Haichao, a professor at Sichuan University's School of Archaeology and Museology, says these fragments were found in 2021 in Sanxingdui's No 7 sacrificial pit, but severe corrosion had left their shape unrecognizable.

Given their fragile condition, the excavation team block-lifted the fragments with the surrounding soil and transferred them to a lab for conservation, he says.

Metallographic and compositional analyses reveal that the fragments are high in nickel — approximately 20 percent — and have a uniform alloy composition, features that cannot be achieved by any known smelting technology from the late Shang period. These characteristics, however, align perfectly with meteoritic iron.

To date, 13 meteoritic iron artifacts have been identified in China, most of which were found in the Central Plains and northern regions, including Beijing, Hebei and Henan provinces. The meteoritic iron artifact excavated from Sanxingdui, the first in Southwest China, is also the largest of its kind in the country, according to the study.

Unlike the Central Plains, where meteoritic iron was commonly used only as inserts in bronze objects, Sanxingdui crafted an entire artifact from meteoritic iron, highlighting a distinctive metallurgical practice, Li says.

"The discovery not only fills a critical gap in the region's metallurgical records, but also provides new insights into early iron use both regionally and globally," he adds.

While the axe-shaped artifact's discovery in a ritual pit suggests cultural significance, its precise function remains uncertain, according to the researchers.

Cut marks on many Sanxingdui bronzes, including masks and vessels, indicate the use of high-hardness tools. This suggests that meteoritic iron objects were used to modify bronze items, though further evidence is needed.

"The specific type of meteorite the artifact came from is also unknown," Li says, adding that further study will focus on high-resolution characterization to determine its exact classification.