Rocks are the portion of the earth’s crust i.e top most layers of the earth having no definite shape and structure.
Rocks are natural hard substance formed from minerals and earth material which are present in rocks. There are three Classification of Rocks according to shape, size, structure, characteristics etc. which are described below.
Rocks are used for different purpose in construction as well as decoration of the structure. Rocks ae used for formation of hard foundation on soling, they are used for construction of statue and ornament.
They are used for the construction of shear wall, retaining walls to make structure stable etc. Beside these rocks are used for electicle device, floor tiles, paving surface, heating device, painting etc.
Classification of Rocks
- A) Geological Classification
- B) Physical Classification
- C) Chemical classification
Among both of the rocks classification, geological classification of rocks are mostly based on the mode of formation and location while physical classification of rocks mostly based on the structure and appearance of the rocks.
Now, let us discuss each Classification of Rocks in detail.
A) Geological classification
1. Igneous Rocks
These are formed as a result of the solidification of molten mass (magma) lying below (or) above the earth’s surface. The colour of the igneous rock depends upon the amount of felspar present in it.
Characteristics of Igneous Rocks
- Generally, magma consists’ of “Quartz, Mica and Felspar”.
- The texture of the rock is greatly influenced by the rate of cooling magma.
- These rocks are mostly crystalline, glassy or fused texture.
Example: Granite, Syenite (Deep rock/Plutonic), and Dolerite, Basal (Surface rock/ Effusive volcanic)
2. Sedimentary Rocks
Sedimentary rocks are also known as “Aqueous or Stratified Rocks”.
Characteristics of Igneous Rocks
- Sedimentary rocks are formed due to the gradual deposition of materials like salt in water or sands, clay or fragments, or magma.
- The rocks are soft and can be easily split up along the bedding as well as normal planes.
Examples: Dolomite, Magnesite, Gypsum (Chemical Deposit), Limestone, Shale, Chalk (Organogeneous rock), Sandstone (Fragmental rocks).
3. Metamorphic Rocks
These are formed from Igneous or Sedimentary rocks as a result of the action of the earth’s movements, temperature changes, liquid pressure, etc.
Example of different types of Rocks.
| A) Igneous rock | B) Metamorphic rock |
| Granite , Syenite Dolerite, Basalt | Gneiss, Schist |
| C) Sedimentary Rock | D) Metamorphic Rock |
| Limestone , Dolomite, Sandstone, Shale | Marble, Quartzite, Slate |
B) Physical Classification
1. Stratified Rocks:
Stratified rocks show distinct layers along which rocks can be split or broken.
Example: Sandstone, Limestone, Shale, Slate, Marble, etc. (i.e. Almost all sedimentary and sediment rocks are stratified rocks).
2. Unstratified Rocks:
Unstratified rocks do not show any stratification and cannot be easily split into thin layer like stratified rocks. Almost all igneous rocks are unstratified rocks.
3. Foliated Rocks:
Foliated rocks have a tendency to split up only in a definite direction. Example: Almost all Igneous-Metamorphic rocks are foliated rocks.
C. Chemical Classification
1. Silicious Rocks:
The principal constituent is Silica (SiO2 ), i.e. Sand.
- These rocks are very hard and durable.
Example: Almost all Igneous-Metamorphic rocks.
2. Argillaceous Rocks:
The principal constitute is clay (Al2O3)
- These are hard and Brittle.
Example: Slate, laterite (a sandy clay stone) etc.
3. Cal-carious Rocks:
The principal constituent is Lime (CaO)
- These are good surface texture.
Example: Dolomite, Limestone, Marble, etc.
Some uses of Different Rocks/Stones and their Characteristics
| S.N. | Rocks/Stone | Uses/Suitability | Characteristics |
| 1 | Granite or Syenite | 1. Most suitable for important Engineering works. 2. Used for Exterior facing of buildings. 3. Fine grained granite offers high resistance to weathering. | 1. It can be easily polished and worked . 2. Excess of felspar causes early decay. 3. Water absorption <1% |
| 2 | Marble | 1. Suitable for monuments, ornamental works 2. Flooring and decorative works (Electric switchboards etc.) | 1. Specific gravity = 2.65 2. Crushing strength = 70 N/mm2 |
| 3 | Basalt | 1. Road metal and Concrete aggregates | 1. High Specific gravity = 2.6-3 2) High Crushing = 150-190 N/mm2 |
| 4 | Quartzite | 1. Railway Ballast, Roa metal and C.A. | |
| 5 | Slate | 1. Used in Cisterns, Damp proving’s 2. Excellent roof covering material | 1. Specific gravity = 2.89 2. Crushing strength = 77.210 |
| 6 | Sandstone | 1. Tile stone (Roofing), Flag stone (Paving) 2. Girt (heavy work), Natural (Ornamental) | 1. 2.65-2.95 2. 65 N/mm2 3. Quartz + time + Silica |
| 7 | Limestone | 1. Flooring, roofing and pavings and walls 2. In the manufacture of lime and cement | 1. 2-2.75, 55 N/mm2 2. Affected by frost and atoms |
| 8 | Gneiss | 1. Rough stone works (like street pavings) | 1. Quartz + felspar (strong + durable) |
| 9 | Laterite | They are very good metal, so they can be used for electrical device. | Sandy clay stone |
| 10 | Kankar | Mostly used for Foundation of buildings. | 1. They are Irregular in shape. 2. Impure lime stone |
| 11 | Moorum | They are used for Fancy paths, like garden walks etc. | The are formed by Decomposed laterite. |
I hope this article on “Classification of Rocks” remains helpful for you.
Civil Concept
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What are the qualities of good building stone?
Stone Masonry Wall | Types, Advantages, Construction Process
Types of stones used in the construction | Basalt, Granite, Limestone
