‘Unique’ Cave Pearls Containing Ancient Artifacts Discovered in Tunnel

Researchers have found a “unique” collection of “cave pearls”—some of which contain archaeological artifacts—in an ancient tunnel, a study has reported.

Cave pearls are a type of “speleothem”—a term referring to various mineral formations that occur inside caves, including stalactites and stalagmites.

Spherical in shape, cave pearls are typically small, measuring between 0.1 millimeters and 30 centimeters (around 12 inches) across.

Found in shallow pools of water saturated with the mineral calcite, they are usually detached from the floor, walls or ceiling of the cave, unlike most speleothems.

In the latest study, published in the journal Archaeometry, a team of researchers report the discovery of 50 cave pearls in an ancient tunnel located in the Jerusalem Hills of Israel.

Cave pearls have previously been found on most continents, yet they are “very rare” in the Southern Levant region, the authors said, adding that the recently uncovered assemblage is the largest and richest ever found in the region.

Cave pearls are known to form around a nucleus, which can be made from a number of materials, such as rocky fragments, mud pieces, blue algae, wood shreds and animal bones.

But some examples in the recently discovered assemblage appear to have formed around archaeological artifacts—representing the first time scientists have documented such a phenomenon.

Compared with other speleothems, cave pearls are often relatively young in age—in the order of hundreds of years—due to their rapid growth rate.

“Until the current study, cave pearls were neither found in an archaeological context nor used for archaeological research,” the study authors wrote in the paper.

The research team stumbled upon the assemblage of 50 cave pearls while conducting investigations in the Joweizeh spring tunnel in the Jerusalem Hills. A spring tunnel is an ancient man-made construction designed to extract water from perched aquifers—a type of subterranean water-bearing rock layer.

More than 210 spring tunnels are known in the mountainous area of the Southern Levant, demonstrating perhaps the densest region of such constructions worldwide.

The Joweizeh spring tunnel is one of the longest and most ancient found so far in the Southern Levant. The tunnel is divided into two main segments and has an overall length of more than 760 feet.

Previous evidence had indicated that the origins of the structure dated to the Late Iron Age II, which typically refers to the period in this region spanning from the late 10th century B.C. to the early 6th century B.C. It was possibly constructed as part of a royal mansion.

The research team were not looking for cave pearls. But during a survey conducted in Joweizeh in 2017, they found evidence of antiquity looting and an opening leading to a previously sealed segment that splits from the main tunnel southward. The newly revealed segment is around 23 feet long and is clogged up with soil and debris.

It was within this segment and the associated debris that the team found the cave pearl assemblage alongside an intact oil lamp, likely dating to the 3rd–4th centuries A.D.

The researchers subsequently conducted analyses of the cave pearls in order to understand their form, composition and age. They found that 14 of the 50 had formed around pottery sherds—two of which appeared to originate from ceramic lamps—while the nucleus of two others consisted of ancient plaster fragments.

Charcoal samples extracted from the plaster nuclei of two of the cave pearls were dated to around the time of the Hellenistic period (332–63 B.C.). Dating work on the pottery nuclei revealed that most of them probably also date to the Hellenistic period, or the later Roman to Byzantine periods, which spanned from 63 B.C. until the early Islamic conquests of the 7th century A.D.

But there were a couple of exceptions, including one sherd (known as J-14) that appears to be associated with earlier dates stretching back in time from the Hellenistic period, to the Persian or Babylonian periods—or perhaps even the Iron Age.

The latest results support multiple periods of tunnel usage and cave pearl formation, according to the authors. The study provides evidence of a reconstruction campaign of the tunnel that took place during the Hellenistic period and was probably carried out by the light of lamps.

The pottery nuclei data and other finds presented in the study support a Hellenistic to Byzantine date for the usage of the tunnel, although J-14 points to an earlier period spanning from the Iron Age to the Hellenistic era.

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Reference

Yechezkel, A., Vaknin, Y., Cooper‐Frumkin, S., Ryb, U., Shaar, R., Gadot, Y., & Frumkin, A. (2024). Dating an ancient spring tunnel using archaeological artefacts functioning as nuclei of cave pearls. Archaeometry. https://doi.org/10.1111/arcm.13031