Foliation
The foliation is a feature that many metamorphic have rocks. Similar to the stratification of the sedimentites , the foliation is a layered (planar) texture of the rock. In contrast to stratification, however, foliation is not the result of a deposition process, but rather is caused by tectonic processes that affect the rock with high pressure and temperature. Foliage surfaces do not necessarily have to run parallel to existing sedimentation levels. In the case of their non-parallel arrangement, one speaks of transversal foliation .
Minerals that have a very strong tendency to form flat structures ( e.g. mica , clay minerals , representatives of the chlorite group ) regulate themselves under the directed pressure of the metamorphic process in such a way that the areas of greatest crystal growth, namely the edges, are exposed to the least pressure, since this is energetically the most favorable for crystal growth. The largest areas of these minerals are therefore perpendicular to the direction of the directed pressure. The cleavage areas created in this way form a system of fractures in many rocks as a result of further mechanical influences, which can significantly influence the stability of the rock body concerned. This fact has geotechnical and technical importance.
Rocks, in which these features typically occur, are primarily the clay slate , furthermore quartzites or prasinites . Occasionally, marbles , sometimes called cipollino , have this property.
If the structure in the rock shows changing layers of significantly different composition, one speaks more of a banding . This is found mainly in higher grade metamorphic rocks.
See also
literature
- Gerhard H. Eisbacher: Introduction to Tectonics . 2nd edition, pp. 175-181, Enke, Stuttgart 1996; ISBN 3-432-99252-1
- Wolfhard Wimmenauer: Petrography of igneous and metamorphic rocks . Ferdinand Enke Verlag, Stuttgart 1985, p. 245 ISBN 3-432-94671-6