Tectonite
Encyclopedia
Tectonites are metamorphic
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...

 or tectonically deformed
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...

 rocks
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

 whose fabric reflects the history of their deformation, or rocks with fabric
Fabric (geology)
In geology, a rock's fabric describes the spatial and geometric configuration of all the elements that make it up.-Types of fabric:* Primary fabric — a fabric created during the original formation of the rock, e.g...

 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 phyllosilicates or graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...

. Slender prismatic crystals such as amphibole
Amphibole
Amphibole is the name of an important group of generally dark-colored rock-forming inosilicate minerals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures.-Mineralogy:...

 produce a lineation in which these prisms or columnar crystals become aligned.

Classification

  • S-tectonites (from the German, Schiefer for schist) have a dominant planar fabric
    Fabric (geology)
    In geology, a rock's fabric describes the spatial and geometric configuration of all the elements that make it up.-Types of fabric:* Primary fabric — a fabric created during the original formation of the rock, e.g...

     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
    Mylonite
    Mylonite is a fine-grained, compact rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. It is classified as a metamorphic rock...

    .
  • 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 mylonite
    Mylonite
    Mylonite is a fine-grained, compact rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. It is classified as a metamorphic rock...

    s are L-S tectonites consistent with a simple shear
    Simple shear
    In fluid mechanics, simple shear is a special case of deformation where only one component of velocity vectors has a non-zero value:\ V_x=f\ V_y=V_z=0And the gradient of velocity is constant and perpendicular to the velocity itself:...

    deformation.
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