Cataclastic
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Cataclastic rocks contain angular fragments formed by cataclasis. Cataclasis is a deformation of the rock caused by fracture and rotation of aggregates or mineral grains.
The term cataclastic refers to the structure produced in a rock by the actions of severe mechanical stresses that occur during metamorphism. Characteristic features of cataclastic metamorphism include the bending, breaking, and granulation of minerals.
Cataclastic structures, also called mortar structures, or "porphyroclastic," are granites and gneisses that are produced by dynamic metamorphism of crystalline rock, and are characterized by mica-free aggregates of small finely-crushed grains of quartz or feldspar that fill the interstices between larger individual relicts and thus resemble stones set in mortar.
Porphyroclastic refers to the metamorphic texture characterized by large strained metacrysts within a finely recrystallized matrix of neoblasts that are free of strain.
