Something Digs Intricate Tunnels in Garnets. Is It Alive?

Microscopic tubular structures found within red garnets may be caused by the burrowing of microorganisms.

Deep red garnets are found all over the world, from Thailand and Sri Lanka to the Adirondacks. They’re even the state gem of New York.

The stones that make their way into rings and necklaces must have a flawless interior. But sometimes garnets are marred with intricate traceries of microscopic tunnels. When Magnus Ivarsson, a geobiologist at the Swedish Museum of Natural History, first saw these tunnels, he wondered what could be making them.

After Dr. Ivarsson and his colleagues traveled to Thailand, they found that an assortment of evidence contradicted standard geological explanations for how the cavities might be formed. In a paper in PLOS One, the researchers are floating a new hypothesis: Perhaps what’s making the tunnels is alive.

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From the beginning, the researchers looked for alternative explanations. One of the most promising was that grains of another stone wore their way through the garnet. However, the mineral doing the tunneling must be harder than the surrounding substance, and garnets happen to be very, very hard. About the only things that could do that to garnet are diamonds or sapphires. But those aren’t present in significant quantities where these garnets were found, said Dr. Ivarsson. In that area, “there is basically no mineral grain that can be propelled through a garnet like that,” he said.

Furthermore, the tunnels branch and connect with each other in a very unusual pattern, looking a bit like the structures made by some kinds of single-celled fungus colonies. When the researchers cracked the garnets open, they tested the insides of the tunnels and found signs of fatty acids and other lipids, potential indicators of life.

It’s not unheard-of for microorganisms to live in rocks — endoliths, as such creatures are called, have been found living encased within sandstone in the Dry Valleys of Antarctica, among other places. Endoliths can get nutrients from water percolating through rock, or perhaps even dissolve it to feed themselves, while living safely.

At the moment, the researchers’ best guess for the origins of the tunnels goes like this: At first, normal wear-and-tear on the surface of a garnet creates divots. Microorganisms, probably fungi, can colonize these hollows. Then, if the stone is the best nearby source for certain nutrients, such as iron, perhaps they use an as-yet mysterious chemical reaction to burrow deeper, harvesting sustenance as they go.

“I think there’s a two-step process, a superficial weathering, then an organism takes over,” said Dr. Ivarsson.

No one, not even Dr. Ivarsson, is totally convinced of the explanation yet. “There’s definitely work to be done,” he said.

The team did not try to extract living organisms from the stone this time around, and indeed is not sure whether the creatures that made the tunnels would still be present within. They also don’t know whether the process may have occurred millions of years ago in the gems where it is seen, or if it occurred more recently.

The next step would be to take organisms directly from the tunnels or the soil near where the stones were found and grow them in the lab. Then it would be possible to see whether they can actually carve their way through fresh garnet — or if the origin story of these mysterious structures must lie somewhere else.

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