DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Rock crystal microstructure. Light micrograph of a thin section through a piece of the rock mineral feldspar. Distinctive folds and 'hinge' lines are seen. These are crystalline microstructures called knee-folds. They occur in thinly layered minerals and rocks, like this feldspar. Feldspar is a very common group of aluminium silicate minerals that makes up many igneous and metamorphic rocks. These kinks in the crystal structure will have formed in response to intense compressive forces, with the kinks or slips occurring between different layers of the mineral.
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