A mylonite showing a number of (rotated) porphyroclasts: a clear red garnet left in the picture while smaller white feldspar porphyroclasts can be found all over. Location: the tectonic contact between the autochthonous Western Gneiss Region and rocks of the allochthonous Blåhø nappe on Otrøy, Caledonides, Central Norway.

A porphyroclast is a clast or mineral fragment in a metamorphic rock, surrounded by a groundmass of finer grained crystals. Porphyroclasts are fragments of the original rock before dynamic recrystallisation produced the groundmass. This means they are older than the groundmass. They were stronger pieces of the original rock, that could not as easily deform and were therefore not or hardly affected by recrystallisation. They may have been phenocrysts or porphyroblasts in the original rock. Mylonite is a fine-grained, compact rock without cleavage or crystals. ... Garnet is a group of minerals that have been used since the Bronze Age as gemstones and abrasives. ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... The tectonic plates of the world were mapped in the second half of the 20th century. ... Look up autochthonous in Wiktionary, the free dictionary. ... In geology, rocks or sections or units of rocks which have been moved from their original site of formation are called allochthon (from greek allo = other, and chthon = earth). ... The Caledonian orogeny is a mountain building event recorded in the mountains and hills of northern Scotland, Ireland, England, Wales, and west Norway. ... In geology, the term clastic refers to sediments formed from fragments of pre-existing rock. ... Minerals are natural compounds formed through geological processes. ... Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. ... The matrix or groundmass of rock is the fine-grained mass of material in which larger grains or crystals are embedded. ... Quartz crystal Copper(II) sulfate and iodine crystal Synthetic bismuth crystal Insulin crystals Gallium, a metal that easily forms large single crystals A huge monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for the megajoule laser of CEA. In chemistry and mineralogy, a crystal is a solid... Dynamic recrystallization (DRX) is a type of recrystallization process, found within the field of metallurgy. ... It has been suggested that Tensile strength be merged into this article or section. ... In engineering mechanics, deformation is a change in shape due to an applied force. ... Example of phenocrysts in rhomb porphyry from the Oslo rift area in Norway A phenocryst is a relatively large and usually conspicuous crystal formed in the mass of a porphyritic igneous rock. ... A porphyroblast is a large mineral crystal of metamorphic origin which has grown within the finer grained groundmass of a metamorphic rock as a response to the stresses or heat of metamorphism. ...

Porphyroclasts are often confused with porphyroblasts. These are also large crystals in a finer matrix, but they grew after deformation took place and after the matrix was formed. The matrix or groundmass of an igneous rock consists of fine grained often microscopic crystals in which larger crystals (phenocrysts) are embedded. ...

In strongly deformed rocks porphyroclasts are often rotated by the shear stress in the rock. Their shape can be used to determine the direction of the shear. A sphere rotating around its axis. ... Shear stress is a stress state where the stress is parallel to a face of the material, as opposed to normal stress when the stress is perpendicular to the face. ...