A network of tunnels forming unique patterns in red garnet gemstones may have been created by endolithic fungi. The New York Times reported on a recent PLOS One article proposing the hypothesis. Endoliths bore into rocks or minerals to use the substrate as a protective habitat, for trophic reason or both. Examining the physical markings left by an endoliths in fossils can provide clues to the type of organism that utilize the substrate and why organism may utilized a particular substrate. Alternatively, abiotic processes could also cause complex tunnels.
What makes the tunnels observed in red garnets so unique is that these gemstones are very hard and are found in a low-nutrient environment (river sediment). An abiotic force pushing into the garnet stone is unlikely since it would require the material exerting the pressure to be a least the strength of diamond. Chemical weathering is unlikely because it would produce flaking, shallow pit or erosion with a polygon appearance and not the intricate tunneling observed. When the pattern of the tunnels was analyzed under with various microscopy methods, including scanning electron microscopy (SEM) and synchrotron-radiation X-ray tomographic microscopy (SRXTM), frequent branching and anastomosis were observed similar to the mycelium pattern of fungi. Also, intact fatty acids were detected in the interior of the garnet. The researchers go on to suggest that garnets may provide a rare source of Fe2+ in a nutrient poor river sediment environment and a possible trophic reason for a fungus to utilize the gemstone as habitat. The evidence for what caused the tunnels is not definitive. Nonetheless the existing burrows could provide a habitat for potential endoliths.
Ivarsson, M., Skogby, H., Phichaikamjornwut, B., Bengtson, S., Siljeström, S., Ounchanum, P., … & Holmström, S. 2018. Intricate tunnels in garnets from soils and river sediments in Thailand–Possible endolithic microborings. PloS one, 13(8), e0200351. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0200351