Metamorphic rocks are defined as a group of igneous or sedimentary rocks that were subjected to a set of geological processes that led to a change in their mineral composition and original shape, which resulted in the emergence of metamorphic rocks that include new properties. It also requires the transformation process to occur while the rock is in the solid state without any melting taking place.
Characteristics of metamorphic rocks
1- Metamorphic rocks have some characteristics that distinguish sedimentary or igneous rocks. 2- It may contain some sedimentary structures that accompany the igneous rock, such as neem marks and stratification, in addition to fossils. In the form of blocks that retain some of the properties of igneous rock, such as its distinctive structures or mineral content. It has economic importance such as talc and chromite.
5- The rocks of regional transformation such as slate, schist and gneiss are characterized by the presence of clear foliation, and it is considered one of the most famous and most widespread types.
6- The metamorphic rocks are located in the tectonically active areas in the form of belts extending perpendicular to the direction of movement of the huge rock masses.
1- Heat: 2152 Increasing the temperature leads to the recrystallization of some of the minerals that make up the rock, and then the cohesion of some of the rocks increases. Its crystals become more hard and the rock becomes a new shape. And if the composition has not undergone any change by the influence of heat 2152, examples of which are: 2018 Quartzite and marble.
2- Pressure: The increase in pressure causes the grains that make up the rock to reorganize themselves, converging and stacking in a direction perpendicular to the direction of pressure, and this is called wave pressure. There is another type in which the effective forces of pressure in all directions (homogeneous pressure) and leads to a reduction in the volume of the rock and thus an increase in the specific weight of the minerals that make up it, and this type is accompanied by an increase in temperature due to the presence of the influence on great depths below the surface of the earth.
2152 3- Chemically active solutions: The chemical activity of hot liquids, solutions, vapors and gases associated with pyrotechnic activity plays an important role in substituting elements for each other, leading to the emergence of new mineral compounds in addition to the recrystallization that usually accompanies this thermal activities. All this leads to changing the mineral composition and thus the emergence of metamorphic rocks.
Types of metamorphism
This type occurs as a result of the influence of the rocks adjacent to the igneous objects by the heat emitted by these objects, so the parts in contact with them become subject to recrystallization Its mineral components, and examples of these rocks are quartzite, and marble.
It is effected by the directional pressure associated with ground movements such as folding and cracking. , which leads to the crushing or grinding of some rock components or to agglutination of others in a direction perpendicular to the prevailing pressure direction, an example of this transformation: melonite rocks and kata clast. 2152 3- Thermodynamic transformation
It is sometimes called the regional shift, where the effect is joint for both heat and pressure wave, and because it affects large areas, it is called the regional shift. The minerals that make up the rock tend to be stacked in parallel belts perpendicular to the direction of pressure. An example of this is metamorphism: schist, slate, phyllite, and gneiss.
Metamorphic rock tissues
2152 1- Non-foliated tissue
This type arises by thermal transformation that leads to the recrystallization of the mineral components of the original rock before the transformation, and that As the temperature rises, the shape of the granules does not change before and after the transformation, although it can increase slightly in size to fill the voids, if any. When there are large crystals surrounded by smaller crystals, the tissue in this case is called “porphyroplast.”
2- Foliate tissue
characterized This fabric is in the presence of rows of crystals of minerals that make up the rock, stacked in the form of parallel chips or belts that are perpendicular to the direction of pressure that prevailed during the transformation process, and the temperature contributes to this process. And the foliated tissue is divided into four types: 2152
1- The slate texture: does not exceed a diameter Granules on 1/2018 mm.
2152 2- Fleet tissue: 2018 The diameter of the particles ranges from 1 /2018-1/16 mm. 2152 3- Chistose tissue : 2018 The diameter of the particles is more than 1/ (mm and may reach 1 mm. 4- Mesozoic tissue: granules with a size of more than 1 mm.
3- Dynamic Compression Fabric2152
It occurs in the rocks of melonite and kata clast with a dynamic transformation, where it arises by the effect of wave pressure that results from the effect of ground movements that cause cracking and folding.
Minerals react differently under pressure. Some of them respond completely and turn directly into powder, resulting in the melonite texture, while others degrade m to a lesser extent and the rock components break to varying degrees, resulting in the kata clast fabric, as well as some that show resistance to crystal agglutination in the form of longitudinal lenses in a direction perpendicular to the pressure, resulting in the flaser fabric.