Dicuss some important metamorphic rock
Answers
Explanation:
Metamorphic rocks started out as some other type of rock, but have been substantially changed from their original igneous, sedimentary, or earlier metamorphic form. Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot mineral-rich fluids or, more commonly, some combination of these factors. Conditions like these are found deep within the Earth or where tectonic plates meet.
Process of Metamorphism:
The process of metamorphism does not melt the rocks, but instead transforms them into denser, more compact rocks. New minerals are created either by rearrangement of mineral components or by reactions with fluids that enter the rocks. Pressure or temperature can even change previously metamorphosed rocks into new types. Metamorphic rocks are often squished, smeared out, and folded. Despite these uncomfortable conditions, metamorphic rocks do not get hot enough to melt, or they would become igneous rocks!
Common Metamorphic Rocks:
Common metamorphic rocks include phyllite, schist, gneiss, quartzite and marble.
Foliated Metamorphic Rocks:
Some kinds of metamorphic rocks -- granite gneiss and biotite schist are two examples -- are strongly banded or foliated. (Foliated means the parallel arrangement of certain mineral grains that gives the rock a striped appearance.) Foliation forms when pressure squeezes the flat or elongate minerals within a rock so they become aligned. These rocks develop a platy or sheet-like structure that reflects the direction that pressure was applied.
Non-Foliated Metamorphic Rocks:
Non-foliated metamorphic rocks do not have a platy or sheet-like structure. There are several ways that non-foliated rocks can be produced. Some rocks, such as limestone are made of minerals that are not flat or elongate. No matter how much pressure you apply, the grains will not align! Another type of metamorphism, contact metamorphism, occurs when hot igneous rock intrudes into some pre-existing rock. The pre-existing rock is essentially baked by the heat, changing the mineral structure of the rock without addition of pressure.
Answer:
Slate:
Slate is an extremely fine-grained metamorphic rock characterized by a slaty cleavage by virtue of which it can be readily split into thin sheets having parallel smooth surfaces. The slaty cleavage is due to parallel arrangement of platy and flaky minerals of the slate under the dominant stresses operating during the process of metamorphism
Schist:
Schists are megascopically crystalline foliated metamorphic rocks characterised by a typical schistose structure. The constituent flaky and platy minerals are mostly arranged in parallel or subparallel layers or bands.
Gneiss:
A gneiss (pronounced as neis) is a megascopically crystalline foliated metamorphic rock characterised by segregation of constituent minerals into layers or bands of contrasting colour, texture and composition. A typical gneiss will show bands of micaceous minerals alternating with bands of equi-dimensional minerals like felspars, quartz and garnet etc
Quartzite:
Quartzites are granular metamorphic rocks composed chiefly of intersutured grains of quartz. The name Orthoquartzite is used for a sedimentary rock of similar composition but having a different (sedimentary) origin, in which quartz grains are cemented together by siliceous cement.
Marble:
Marble is essentially a granular metamorphic rock composed chiefly of recrystallised limestone (made of mineral calcite). It is characterized by a granulose texture but the grain size shows considerable variation in different varieties. It varies from finely sachhroidal to highly coarse grained. Marbles often show a banded structure also; coarse varieties may exhibit a variety of structures.