Igneous, what are they? Igneous is a type of rock which is formed when magma or lava is cooled and solidified. Basically melting is caused by an increase in temperature, pressure decrease, or changes in composition.
Extrusive vs. Intrusive: Intrusive is the type of rock which is cooled slowly, in such rocks we can see a better crystal growth, though extrusive is the type which cooled quickly, in result these rocks have less crystal growth and are fine grained.
Texture (classifications) : Shape, orientation, size and distribution are of the mineral grains and the intergrain relations determine the texture. By checking these aspects we can determine if the rock is an apyroclastic, tuff lava or just a simple lava.
Felsic vs. Mafic: If we look at the igneous rocks from chemical aspect, then we can classify them according to the level of silica. Felsic igneous rocks contain more than 63% SiO2 but the mafic igneous rocks have less amount silica ( 45- 52%) but they have high amounts of metals such iron or magnesium.
Metamorphic rocks: Basically it is the transformation of other types of rock, this process is called metamorphism, it means change in form. In this process protolith under high pressure and temperature is changed in physical and/ or chemical structure.
Contact vs regional: Contact metamorphism is the situation when for example magma becomes in contact with other rocks. Due to the high temperature of the magma and it’s contact with other rocks a metamorphic process happens which is called contact metamorphism. But the regional metamorphism refers to great masses of rock in a wide area. In this situation rocks in depths, under great pressure caused by the weight of the rock layers and the high temperature are metamorphosed.
Foliation: The internal layering of metamorphic rock is known as foliation.
Metamorphic rock textures:
Slaty: is a fine-grained, low-grade regional metamorphism.
schistose: is a medium-grade metamorphism.
gneissose: is high-grade regional metamorphism.
Metamorphic facies: The degrees refer to the temperature and/ or the pressure of when metamorphism happens.
There are 6 facies:
1. Zeolite
2.Greenschist
3. Amphibolite
4. Granulite
5. Blueschist
6. Eclogite
