some sulfide-rich rocks around hydrothermal vents on the seabed can spontaneously ignite without an external flame source.
Hydrothermal vents on the ocean floor release hot, mineral-rich water, which over time leads to the formation of mineral-rich deposits that can become valuable sources of copper, zinc, gold, and silver.
However, these deposits also contain sulfur-bearing minerals that can generate heat when they react with oxygen in the air. If this heat accumulates, the material may spontaneously combust. This was discovered by chance by a research team from the U.S. Geological Survey's Pacific Coastal and Marine Science Center while working on 57 rock samples collected from Eskinaba Trou in the northeastern Pacific Ocean, an area containing mineral deposits associated with hydrothermal vents.
Hot Topics
These samples were collected in 2022 and subjected to freeze-drying to remove water, preparing them for laboratory analysis. During the preparation process, researchers observed that two samples began producing heat and smoke, reaching temperatures exceeding 100 degrees Celsius, and then ignited without an external flame. The heat was evident even before the rocks were crushed.
Experiments to interpret the scene
The scene did not go unnoticed, as the researchers had to interpret it. They resorted to comparing the rocks that caught fire with rocks that did not catch fire, to find out the differences between them, using microscopic examination, chemical analysis and identification of the minerals present in the samples.
The result of this comparison was that the two samples that caught fire were rich in "marcasite", an iron sulfide mineral whose structure is characterized by fine crystals, cracks and voids that may increase its exposure to oxygen.
The researchers then studied the chemical reactions and conducted thermal analyses and tests, concluding that the reaction of marcasite with oxygen can produce heat, and that its accumulation may lead to spontaneous combustion under certain conditions.
Recommendation for further studies
The researchers emphasize that they have not proven that all marcasite-rich rocks ignite. Of 41 samples rich in this mineral, only two ignited, and therefore they recommend further studies to understand the differences between the samples.
They also recommended examining rocks from other marine sites, testing storage, crushing and processing conditions on ships, and suggested studying the possibility of underwater rock fracturing to help dissipate heat.
Tags:
science