Physical and Chemical Classifications of Rocks

classification of rocks


Physical classification mainly depends upon the structure of the rock. it may be classified into the following three categories :

  1. Stratified Rocks
  2. Unstratified or Massive Rocks
  3. Foliated or Laminates Rocks


  • Stratified Rocks: These are the rocks which have distinct layers in their structure i.e. these rocks show a layered structure. Stratified rock possesses planes of stratification and can be easily split up along these planes. The planes are also known as cleavage planes or bedding planes. Limestone, Slate, Shale, Sandstone, Marble are the example of Stratified rocks.
  • Unstratified Rocks: These are the rocks which do not show distinct layers in their structure. They have the compact massive structure . Unstratified rocks cannot be separated into layers.

EXAMPLES : Quaztzite , Basalt etc.

  • Foliated or Lamination Rock : These are the rocks which have the tendency to split up in a definite direction only. Foliated structure is quite common in metamorphic rocks .


Chemical composition is the criterion for this type of classification. Based on it, rock can be divided into following three categories :

  1. Argillaceous Rocks.
  2. Silicious Rocks.
  3. Calcareous Rocks.
  • Argillaceous Rock: The main constituent of these type of rock is clay oralumina. This clay or alumina remains mixed up with siliceous, calcareous and carbonaceous matter in varying proportion. In this type of rocks generally clay content is greater than 50%.

Example : Laterite , slate , Shale etc.

  • Silicious Rocks :  Silica is the predominate constituent in this type of rock . Silica content is more than 50 % in this type of rock . Hardness and durability are main properties of siliceous rocks.

 Example :  sandstone , Granite , Trap , Syenite etc.

  • Calcareous Rocks : The principal constituent of this type of rocks is calcium carbonate or lime . These  rocks are highly sensitive with HCL. So, atmosphere is the main consideration  while using these type of rocks.

Example : Marble , Dolomite , Limestone etc.


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