Tiny defects in common minerals may reveal unexpected patterns in how Earth’s interior moves.
Minerals quietly shape the world around us, from the rocks beneath our feet to the deep interior of the planet. At their core are crystals, orderly arrangements of atoms that repeat in precise, three-dimensional patterns. While these structures may seem rigid, they are far more dynamic than they appear.
Under intense pressure and heat, such as those found deep inside Earth, crystals can bend and flow rather than break. This ability comes from tiny defects known as dislocations, small irregularities in the atomic structure that act like microscopic slip zones. They allow solid rock to slowly deform over time, a process that ultimately helps drive the movement of tectonic plates.
In some crystals, dislocations are abundant, while in others they are rare and difficult to detect. Finding them can be as challenging as searching for a needle in a haystack.
Olivine, the most common mineral in the upper 400 km (about 250 miles) of Earth’s interior, has long been studied for how it deforms. Scientists have identified two primary directions of dislocation movement, labeled “a” and “c.” A third direction, known as “b,” has traditionally been considered uncommon and less important.
A recent study led by a University of Liverpool Earth scientist revisited this assumption. The research aimed to better understand how olivine deforms, a key process that drives plate tectonics, and to identify the types of dislocations involved.
Advanced Microscopy Techniques
The team used Electron Backscatter Diffraction (EBSD), an advanced microscopy method that maps subtle differences in crystal orientation at a microscopic scale.
Their analysis showed that about 17% of the crystals examined displayed deformation linked to the previously underestimated “b” dislocations.
To confirm this result, the researchers turned to Transmission Electron Microscopy (TEM), which can directly image dislocations. By focusing on regions flagged by EBSD as showing “b” slip, they captured detailed images that verified these structures were indeed present.
Professor John Wheeler, George Herdman Professor of Geology at the University of Liverpool and lead author of the study published in Geophysical Research Letters, said:
“Our findings suggest that these dislocations may be more widespread than previously thought, improving our understanding of how the Earth’s mantle deforms.
“Their presence may be influenced by pressure, temperature, and stress levels. Measuring ‘b’ dislocations in natural samples could therefore help scientists determine the depth of deformation and the conditions experienced during it.”
Broader Applications and Future Research
The study also highlights how EBSD can quickly pinpoint areas within crystals that are worth closer examination. Researchers can then use higher resolution tools like TEM to investigate those regions in greater detail.
Professor Wheeler added: “The approach we’ve used could help scientists develop a better understanding of geological processes inside the Earth. It may also have wider applications in materials science. For instance, olivine has crystal similarities to perovskites which have numerous industrial uses. Some materials such as semiconductors contain dislocations because of the manufacturing process which are deleterious to performance, so their abundance and arrangements need to be investigated. ”
Reference: “Olivine Deformation: To B Slip or Not to B Slip, That Is the Question” by J. Wheeler, S. Hunt, A. Eggeman, J. Donoghue, A. Gholinia, Y. Li, E. Tillotson and S. J. Haigh, 17 December 2025, Geophysical Research Letters.
DOI: 10.1029/2025GL117138
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