# Pressure shadow

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A **pressure shadow** (also called **strain shadow**) is a term used in metamorphic geology to describe a microstructure in deformed rocks that occurs adjacent to a relatively large, undeformed particle, such as a [porphyroclast](/source/Porphyroclast). Pressure shadows often appear in thin sections as pairs of roughly triangular regions that are elongated parallel to the foliation around a clast of a different mineral.[1] Pressure shadows that contain fibrous mineral textures are also termed pressure fringes or strain fringes.[2]

## Formation

During deformation, minerals can migrate by plastic flow or may grow by [diffusive](/source/Diffusion) mass transport into the lower-stress regions created by a rigid porphyroclast or porphyroblast.[3]

## References

1. Passchier and Trouw (2005). *Microtectonics*. 2nd ed. Springer. ISBN 978-3-540-29359-0.

1. Müller, W.; Aerden, D.; Halliday, A. N. (2000). "Isotopic dating of strain fringe increments: duration and rates of deformation in shear zones". *Science*. **288** (5474): 2195–2198. [Bibcode:2000Sci...288.2195M](https://ui.adsabs.harvard.edu/abs/2000Sci...288.2195M). [doi:10.1126/science.288.5474.2195](https://doi.org/10.1126/science.288.5474.2195). [PMID 10864865](https://pubmed.ncbi.nlm.nih.gov/10864865)

1. Blenkinsop, T.G. (2007). *Deformation Microstructures and Mechanisms in Minerals and Rocks*. Kluwer Academic Publishers. p. 150. ISBN 978-0-306-47543-6.

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