Rocks types

 What are the 5 types of rock?

How do you classify rocks?

The rocks

 Rocks are solid clusters made of minerals and semi-minerals arranged in the form of crystals of varying size, some of them are large in size that can be distinguished by the naked eye, and some are microscopic in size, and some rocks are devoid of crystals. Rocks are divided according to the way they were formed into three types: igneous rocks, sedimentary rocks, and metamorphic rocks. 

Fiery Rocks 

Igneous rocks are formed as a result of hardening or freeze the molten material in the subsoil ( Almajma ); This is due to gradual and continuous cooling, or rapid and sudden cooling.


Classification of igneous rocks

 Igneous rocks can be classified on several bases, including Silica ratio: Igneous rocks are divided, depending on the percentage of silica in them, into: 

Acid rocks: These are igneous rocks in which the silica content reaches more than (66%), including granite rocks and granodiorite.

 Medium igneous rocks: These are rocks whose silica content ranges from (52 ​​-66%), including diorite rocks and cyanite.

 Basal igneous rocks: These are rocks whose silica content ranges from (40-52%), including basalt rocks and gabbro.

 Igneous rocks above basic: they are rocks in which the percentage of silica is less than (40%), including Pridotite and Donite rocks.

The site of origin: Igneous rocks are divided, depending on the place of their formation, into:

 The subterranean igneous rocks or the Plutonian rocks: they are rocks that hardened at great depths under the earth's surface as a result of gradual and continuous cooling under high pressure, and in the presence of volatile materials, and are distinguished by their coarse texture that consists of large-sized mineral crystals that can be distinguished with the naked eye, examples of which are: granite, diorite, And gabbro.

 Surface igneous rocks (volcanic rocks ): They are rocks that hardened near the surface of the earth as a result of rapid cooling, and their texture is either fine-grained (that is, it contains small mineral crystals) or glassy (that is, it does not contain mineral crystals). 

Interlocking igneous rocks: They are igneous rocks that were formed in a middle area that is neither deep nor shallow, and its texture is of medium graininess, including the new rocks (incisors) and dam rocks.

The properties of igneous rocks 
  • Among the characteristics of igneous rocks are the following: They are not arranged in layers. 
  • The size of its constituent crystals depends on the speed of cooling of the rocks when the cooling is slow, the size of the crystals is large, and sometimes the rocks cool down very quickly, leaving no room for crystals to form from the foundation.
  •  It does not contain pores and is therefore impermeable to water.
  •  Resistance to erosion; So it erodes very slowly.
  •  It does not contain fossils.
  •  It contains silica, magnesium, and iron.
Sedimentary rocks 

Sedimentary rocks are rocks that are formed from grains that were separated from pre-formed rocks as a result of various factors and were deposited, and their parts united together.

Types of sedimentary rocks

Sedimentary rocks are classified into three main types, which are: 

Clastic Sedimentary Rocks: Clastic Sedimentary Rocks: Clastic sedimentary rocks are formed from fragments of other rocks separated from each other due to mechanical weathering processes without undergoing chemical changes, then hardened and fossilized again, and fused to each other under pressure, examples of which are: conglomerates, rocks. Breccia, silt rocks, sandstone, and clay. 

Chemical Sedimentary Rocks: They are sedimentary rocks that are formed when water evaporates in arid lands, leaving behind dissolved minerals. Examples include Chert, dolomite, gypsum, limestone, and rock salt. 

Organic Sedimentary Rocks: They are sedimentary rocks that were formed as a result of the deposition of animal residues, such as bones and shells that contain calcium salts, and plant residues on the seafloor, and with the passage of time they hardened, and their types: amber, bituminous coal or coal Lime, anthracite, peat, and lignite.

Characteristics of sedimentary rocks Among the characteristics of sedimentary rocks are the following: 
  • It contains plant and animal fossils.
  •  It consists of several layers. 
  • It is characterized by brittleness and rapid erosion due to weathering and erosion. 
  • It contains a lot of pores; This enables it to store the groundwater between its layers.
  •  Showing signs of neem; They are forms that are formed due to the continuous movement of sea waves and their hitting rocks.
Metamorphic rocks

 Metamorphic rocks are sedimentary rocks or bullets came under pressure and heat of various chemical processes; This affected its chemical composition, texture, and type of minerals.

Types of metamorphic rocks 

The metamorphic rocks are classified into two types K, namely: 

Foliate rocks: They are rocks that have been transformed as a result of exposure to heat and direct pressure, and appear to be arranged in layers, the most important of which are gneiss, schist, slate, and phyllite. 

Non-leafed rocks: They are metamorphic rocks that are not arranged in layers, and examples of them are: quartzite, hornfels, marble, and novaculite.

Types of mutation The transformation of rocks into new rocks occurs in several ways, including:

Contact or thermal transformation: results from the eruption of igneous masses that burn rocks; This changes the nature and arrangement of its crystals, as occurs when quartz turns into quartzite. 

Scaled or dynamic metamorphosis: It is the most common type of metamorphosis, and occurs when rocks are exposed to severe heat and pressure. This leads to the destruction of some or all of the original tissues of the rocks, and the formation of new minerals and tissues as happens when the clay rock is transformed into slate. 

Fragmentation transformation: It is the transformation that occurs when rocks are exposed to the high pressure during tectonic movements, which leads to breakage and grinding of the minerals that make up it, and the resulting rocks appear as lush as in melonite rocks. 

Burial metamorphosis: occurs when sediment accumulates over sedimentary rocks. This leads to its high temperature and exposure to severe pressure, which changes its mineral composition and the tissues that makeup it.

Hydrothermal transformation: It is a transformation that results from the exchange of minerals between the solutions that surround the rock and the rock itself when exposed to high heat. Examples include the entry of the sodium element and the exit of the calcium element when the basalt is transformed into the rocks.


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