February 21, 2021

What are Schistosity and Rock cleavage?

Are you a student of Mining engineering and geology? Okay, well if you are here then you must have searched about schistosity and rock cleavage. Well, here I am to solve all your doubts about the schistosity and rock cleavage and we will also discuss what is foliation?

When you actually study the metamorphic rocks and their foundation then the study of the upper mentioned terms is really very important. Let’s start discussing the same.

What is Schistosity?

Schistosity is defined as the structural feature of many metamorphic rocks called Schists and signifies that the rock is made up of parallel or subparallel bands or layers of platy and flaky minerals like mica, chlorite, tourmaline, etc. Within these bands may be found enclosed grains or crystals of some other minerals like garnets.

One main point that I would like to mention here is if the minerals grains are perfect in spheres then there will be very few schistosity effects will be shown by the metamorphic rocks.

What causes Schistosity?

Schistosity results due to combined effects of the heat and pressure during metamorphism involving both recrystallization and reorientation of platy minerals as irregular layers or bands. In other words, the structure is the product of combined action of thermal and dynamic metamorphism on a variety of rocks such as shales, granites, and basalts.

The main reason due to which the schistosity happens in the metamorphic rock is that the metamorphic rock formation process is usually happening in the deep and buried earth area.


What does rock cleavage mean?

Rock cleavage is an important and typical structural feature of metamorphic rocks and may be defined as the capacity of the rock to split along certain directions yielding parallel or subparallel smooth surfaces.

What are the rock cleavage types?

When we actually talk about the types of rock cleavage then the two types of division that are most important have been discussed in the following paragraphs. The classifications of the rock cleavage are actually of the two types.

  1. Flow cleavage.
  • It is also called slaty rock cleavage because development of this kind of cleavage generally happens in the slates.
  • This cleavage is developed during metamorphism by parallel arrangements of highly flaky and platy minerals like mica, talc and chlorite.
  • This type of cleavage generally gives appearance of the bedded planes in the rock actually in most cases the it is actually developed cutting across the bedding planes.
  • This type of the cleavage is actually responsible for the several type of dynamic metamorphism.

2. Fracture Cleavage.

  • Fracture cleavage is a type of cleavage that actually developed due to the parallel orientation of the very fine fractures, often referred to as microfractures.
  • In general, this type of rock cleavage generally developed during the process of dynamic metamorphism.
  • It is often difficult to distinguish between two types of cleavage in a hand specimen. The cleavage structure is of great importance in the field mapping of metamorphic rocks as it provides very special information about straucural features like folding.

What is Foliation?

  • Foliation is a broader term explaining the layered structure in the metamorphic rocks and it is often understood to include schistosity and rock cleavage.
  • As we all know that each layer can be thin as a sheet of paper or as thick as over a meter in terms of thickness. The layers actually form in parallel directions to the perpendicular directions of the low pressure to the highest type of pressure.
  • However, the foliation is actually meant as the particular express of segregation of minerals in an alternating manner.
  • The granular minerals make one layer followed by the second layer of flaky or platy minerals both downwards and upwards and the structure is repeated in three dimensions in the entire rock mass.
  • It may be known as the advanced stage of dynamothermal metamorphism in which rock is further segregated into the bands of alternating mineralogical composition.

one most important point about the foliation that I would like to mention about the foliation is that it is generally results due to dynamothermal metamorphism in coarse-grained igneous rocks like granites and sandstone and metamorphic rocks like schists.

I hope you liked this article and all your points will be cleared. Please share the article with your friends if you liked this article for once.

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