Types of Rocks and Classification

What is Rock?

Rock is defined as a solid portion of Earth`s crust that has no definite shape, size, and Chemical Composition. We will further discuss Types of rocks and their classification in detail. 
Also For civil engineers Formation of kind of rock is an essential factor for Foundation Structures

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Classification of Rocks:
  1. Geological Classification
  2. Physical Classification
  3. and Chemical Classification
1)Geological Classification: Depending upon its formation it is classified as:
  • Igneous rocks 
  • Sedimentary rocks
  • Metamorphic rocks
  • Igneous rocks:
The molten mass is called magma. Igneous rocks are formed as a result of the Solidification of molten mass magma laying above or below the earth’s surface.
Properties: These rocks are Hard, Tough, and dense and crystalline Texture.
Minerals: Augite , Felspar, horn blende ,mica,quartz Etc.
Examples: Basalt, diorite, granite, and Trap.
Further Igneous rocks are classified as 

  • Plutonic rocks: These rocks are formed due to the cooling of magma at a considerable depth from the earth’s surface. these rocks are crystalline in nature. These rocks are cooled slowly because of thick covering over the top examples: Basalt, trap, granite, etc.

  • Hypabyssal rocks: These rocks are formed by the cooling of magma at shallow depth from the earth surface In these rocks the cooling is quite quicker than the Plutonic rocks. The structure is crystalline and fine-grained examples: dolerite, apatite, dolomite, etc.
  • Volcanic rocks: These are formed on the surface so the cooling is quicker than the other rocks therefore due to faster cooling they are non-crystalline , Amorphous and glassy in texture. Examples are syenite, periodolite, andesite Etc
  • Sedimentary rocks: These rocks are formed by gradual deposition of rock products on the surface of the earth this process is called the sedimentation process.
Properties: There is a distinct plane of division through which the rock split up.
Examples:Sand stone,lime stone,gypsum,shale,stale etc.


Sedimentary rocks are divided into the following:

  • Residual deposits: These are due to weathering of rocks at same place Which finally settle out and deposit.
  • Sedimentary deposits: These deposits formed are insoluble in water and major racks of sedimentary comes in this category.
  • Chemical deposits: These are Soluble in water and are carried out in water by the suspension.
  • Organic deposits: biological waste deposition is called organic deposition.
  • Metamorphic rocks:

These rocks are formed by the action of earth movements, temperature changes, liquid pressure
of Igneous rocks or metamorphic rocks, there is a heat transfer between the Magma and pressure developed by a load of rocks this process of change is called metamorphism.
There are different types of Metamorphism such as Thermal, cataclastic, plutonic Metamorphism.
Examples:Slate,marble,gneiss etc.

2)Physical Classification: This classification is based on the appearance and structure of the rocks it is classified as:
  • Stratified Rocks
  • Unstratified Rocks
  • Foliated Rocks

  • Stratified Rocks: These type of rocks have distinct plane of division through the rock can split up Generally sedimentary rocks possess this property 
Example: Sandstone, limestone, Slates, etc.
  • Unstratified Rocks: These rocks are opposite of stratified rocks that do not have a distinct plane of division these rocks are granular or compact granular.
  • Foliated Rocks: These rocks split up in well-defined direction As in the case of metamorphic rocks which are formed by extensive heat and pressure. These rocks are also called as laminated rocks
3)Chemical Classification: Based on chemical compositions it is divided into three categories:


  • Silicious rocks
  • Argillaceous rocks
  • Calcareous rocks

  • Silicious rocks: The composition of this rock is silica and these rocks are hard and durable. Examples: Granite, Basalt, Quartzites, syenites, etc.
  • Argillaceous rocks: The main composition of these types of rocks are argil or clay.these rocks are brittle in nature and hard.
  • Examples: Porphyry, laterite, Stale, etc.
  • Calcareous rocks: The main composition of this rock is Lime. These rocks are also durable in nature.Example:Limestone,dolomite,Marble,kankar etc..

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I hope u have understood the all the different types of rocks and also its classification for more info plz more detail or Types of rocks
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