Tiny tunnels in gemstones found to be caused by microbes

Microscopic tunnels in garnet crystals from Thailand appear to have been created by microorganisms boring into the rock, scientists say. 

That’s surprising, says Magnus Ivarsson, a geobiologist from the University of Southern Denmark, who describes the find in the online journal PLOS ONE. Garnet is a very hard mineral, difficult for such organisms to dig into. 

The tunnels were discovered by Ivarsson’s co-author, Bongkot Phichaikamjornwut of Srinakharinwirot University in Bangkok, Thailand, who realised that they were the reason some Thai garnets had poor clarity, reducing their value as gemstones.

Further examination, Ivarsson says, revealed that the tunnels had complex branches and interconnections. They ranged from a few to hundreds of microns in diameter and were as long as several millimetres. 

“You can see them in an ordinary microscope or even a hand lens,” he says, “but we used optical microscopy, scanning electron microscopy, and synchrotron-based X-ray tomography to produce 3-D reconstructions of the tunnel networks.” 

Within the tunnels were organic materials that appear to be remains of the microorganisms that inhabited them … and which most likely formed them. The most likely culprits, he adds, would have been filamentous ones, such as fungi. 

While the microorganisms that bored the tunnels may have started out by exploiting flaws in the gemstones, he says, once the process began it appears to have been largely produced by the organisms themselves. 

“There are just no known abiotic processes that can explain all the features of these tunnels,” he says, citing their interconnection as an example.

The find is important because, to date, garnet is the hardest mineral discovered into which microorganisms have been found able to bore. It’s also another indication of the diverse ways in which life can survive, not just on the surface, but in the heart of buried rocks.{%recommended 1194%}

The microorganisms that bored the tunnels, Ivarsson’s team suggests, may have been seeking iron, one of the elements in certain types of garnet, which is in poor supply in the sediments in which the garnets were found. 

“Life is inventive,” Ivarsson himself notes. 

The find, he adds, requires paleontologists to expand their understandings of how to identify microbial trace fossils. “We need to be more flexible in the future,” he says.

And it’s not just paleontologists who need to take note. 

“In 2020,” he says, “NASA, ESA, and the Chinese space organisation will send three separate missions to Mars to look for signs of life, including trace fossils. A few years back, tunnels like this would have been dismissed as abiotic, but today we know better.”