Garnets are rather beautiful little things, particularly when they’re pristine and sizeable enough to be classed as gems. These products of geological extremes turn up in all sorts of environments all over the world, but there’s something strange about those found in riverbeds and soils in Thailand.

Plenty of them appear to have little hollow tubes running through them, a value-decreasing property that was previously blamed on chemical or geological processes. A new PLOS ONE study, however, has an eye-catching new hypothesis as to where these tunnels came from: burrowing microorganisms.

At this point, it’s entirely unclear what type of lifeform specifically may have made these tunnels, and the evidence on which this idea is based still lacks a smoking gun. If the researchers are correct, though, this would make it the first time that such biologically produced tunnels have been found within gemstones.

These intricate tunnels form odd, somewhat chaotic patterns, not conforming to the planes that course through minerals that are forged according to physical and chemical laws.

Some chemical weathering may be involved, but the authors’ paper suggests that to look like these tunnels do, they need “the involvement of an agent that controls the direction.” Garnet is also resistant to physical and chemical weathering by even extremely tough minerals, which certainly implies that life found a way instead.

It’s certainly hard to shake the fact that they sure look like tunnels found in a wide range of environments that were bored out by biological entities. The tunnels are incredibly small, which suggests they could have bacterial architects, but certain types of fungi and even algae could also fit the bill.

Significantly, there’s plenty of organic matter within these garnet tunnels, and a highly sensitive spectroscopy technique revealed them to be decidedly complex. Some appear to be fatty acids, the type that’s found in cell membranes used by various organisms.

The reworking and general messing up of sediments by living things is known as bioturbation. It’s most common among small invertebrates, such as worms, but a wide range of critters have been doing it for hundreds of millions of years. It serves multiple purposes, including the need to hide from predators, dig for prey, have somewhere you can anchor to as you nab food that’s passing by, and so on.

The mystery, garnet-loving critter would have been – or remains, if it still exists – an endolith, a type of lifeform that lives in a solid, rock-like substance, which includes things like calcareous shells. They get there by boring, which is sort of a hardcore version of bioturbation.

Endoliths tend to be extremophiles, and frequently live off minerals contained within said environments, like iron – something this garnet has in abundance. There are thousands of species alive today, found as high up as the Alps to within the frigid, dry realms of Antarctica, and they’re represented in the fossil record too.

Before we all get a bit carried away, it must be said that this is not an open-and-shut case, and the University of Southern Denmark-led team underscore this throughout the paper.

Although those organic compounds are oddly complex and found on garnet surfaces, rivers are rich in organics, so it’s possible that they were washed into pre-existing tunnels. There’s also, of course, no source organism, and all the paper’s inferences as to why something would want to dig these tunnels in the first place are (knowing) speculations, but little else.

It’s possible that these could be weathering features that we just don’t understand yet, and the team emphasize that any biological explanation needs “careful and critical consideration.” They also note, however, that “the only known natural processes that can form anastomoses in three dimensions are biological.”

Lead author Dr Magnus Ivarsson, a geobiologist at the Swedish Museum of Natural History, told IFLScience that the next step is to try and isolate any DNA or RNA from within the garnet tunnels.

“With such an approach, we hope to identify the responsible microbe – or microbes – isolate them, grow them and use them in laboratory experiments to see if they actually can dissolve garnets and produce these structures,” he explained, adding that he hopes they aren’t just trace fossils of a bygone organism.

Until then, the origin of these tunnels remains an open question – but one with a potentially exhilarating answer.