Minerals form the building blocks of almost everything on Earth. They are made up of crystals - regular, repeating atomic structures that fit together like a three-dimensional pattern.
When minerals deform, their normally ordered crystal lattices develop linear imperfections known as dislocations. These are small breaks or shifts in the atomic arrangement that allow crystals to change shape under stress.
Some deformed crystals contain large numbers of dislocations, while in others they are sparse and searching for them is like looking for a needle in a haystack.
In olivine, the most common mineral in the upper 400km of the Earth, scientists have long recognised two main directions in which these dislocations move. These are known as "a" and "c". A third direction, called "b", has generally been considered rare and relatively unimportant for deformation.
A new study led by a University of Liverpool earth scientist examined olivine to better understand how it deforms, a process which enables plate tectonics, and what types of dislocations occur.
Using an advanced electron microscope technique called Electron Backscatter Diffraction (EBSD), the team analysed subtle variations in crystal orientation at the microscopic scale.
Their results revealed that a significant proportion of the crystals studied - around 17% - showed evidence of deformation involving the previously overlooked "b" dislocations.
To check this unexpected finding, the researchers then used Transmission Electron Microscopy (TEM) to directly image dislocations in areas identified by EBSD as showing "b" slip. These detailed images provided further confirmation of their presence.
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."
The study also demonstrates how EBSD can be used to rapidly identify regions of interest within crystals, allowing researchers to target areas for more detailed investigation using higher-resolution techniques such as TEM.
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."
The paper, "Olivine Deformation: To B Slip or Not to B Slip, That Is the Question" (/doi.org/10.1029/2025GL117138) is published in Geophysical Research Letters.
Image: Electron microscopy characterization of b dislocations in olivine color coded according to Z direction in crystal coordinates.
