Mica fish is a term used to describe a type of deformational structure that is commonly found in metamorphic rocks. The name “mica fish” comes from the shape of the structure, which resembles a fish with a head and tail.

Mica fish structures are formed when platy minerals, such as mica, are oriented parallel to the direction of stress during deformation. The minerals are stretched and pulled out into thin, elongated shapes, creating a structure that looks like a fish with a head and tail. The “head” of the fish is usually thicker and wider than the “tail”.

Mica fish structures can provide valuable information to geologists about the direction and intensity of deformation during the metamorphic process. By studying the orientation and shape of the fish structures, geologists can determine the direction of the applied stress, as well as the degree of deformation that the rock has undergone.

Mica fish structures are commonly found in rocks that have undergone regional metamorphism, which is a type of metamorphism that occurs over a large area due to tectonic forces. They can be found in a variety of metamorphic rocks, including schist, gneiss, and phyllite.

Mica fish, a special type of porphyroclasts, are single crystals of mica with a lenticular or parallelogram shape. They are common in mylonites derived from micaceous quartzites and granitoid rocks. Mica fish are frequently used to determine the sense of shear in a mylonite zone.