Tectonites are

metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

or tectonically deformed rocks whose fabric reflects the history of their deformation, or rocks with

fabric Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, and different types of fabric. At first, the word "textiles" only referred to woven fabrics. However, weaving is no ...

that clearly displays coordinated geometric features that indicate continuous solid (ductile) flow during formation. ''Planar foliation'' results from a parallel orientation of platey mineral phases such as the

phyllosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dio ...

s or

graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...

. Slender prismatic crystals such as

amphibole Amphibole ( ) is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...

produce a ''lineation'' in which these prisms or columnar crystals become aligned.Best, Myron G., ''Igneous and Metamorphic Petrology'', Wiley-Blackwell, 2nd ed. 2002, p. 448 Tectonites are rocks with minerals that have been affected by natural forces of the earth, which allowed their orientations to change. This usually includes recrystallization of minerals, and the foliation formation. Tectonites are studied through structural analysis and allows for the determination of two things: *The orientation of shearing and compressive stresses during (dynamic) metamorphism *The later (or final) stages of metamorphism According to the nature of mineral orientation, there are three main groups of tectonites, L-tectonites, S-tectonites, and L-S tectonites. The different types reflect on the different ways that matter moves.

Classification

*''S-tectonites'' (from the German, ''Schiefer'' for schist) have a dominant planar

and may indicate a flattening type of strain. This may also be due to a lack of minerals capable of giving a lineation e.g. in a phyllonite. *''L-tectonites'' have a dominant linear fabric and generally indicate a constrictional type of strain. This may be due to a lack of platey phases. *''L-S tectonites'' have equally developed linear and planar fabric elements and may indicate a plane strain deformation. Many mylonites are L-S tectonites consistent with a simple shear deformation.

References

Structural geology Metamorphic rocks {{Metamorphic-rock-stub