Classification of Stones

CLASSIFICATION OF STONES

In general stones used for civil construction works may be classified into the three ways.

1. GEOLOGICAL CLASSIFICATION

Geological classification is based on the mode of formation. On the basis of Geological formation stones are classified into three main forms namely igneous, sedimentary and metamorphic.

❖ Igneous Rocks: Igneous rocks are formed by cooling and solidification of the molten mass lying above or below the surface of the earth. In general igneous rocks are strong and durable. Ex: Granite, trap and basalt. Granites have crystalline surface since they are formed by slow cooling of the molten mass under thick layer on the top surface. Non-crystalline and glassy textures are formed by the cooling of the molten mass at the top surface. Ex: Basalt and trap.

❖ Sedimentary Rocks: Sedimentary rock properties differ considerably based on the nature of sediment and bonding between the sediment and grains. These rocks thus formed are fine grained, more uniform and dense in their nature. In general they represent a bedded or stratified structure. Ex: Sand stones, lime stones, mud stones, chalk etc.

❖ Metamorphic Rocks: Metamorphic Rocks are formed from igneous and sedimentary rocks, since they undergo changes because of metamorphic action of internal heat and pressure. Due to the metamorphic action, granite changes to greisses, trap and basalt becomes schist and laterite, lime stone changes to marble, sand stone becomes quartzite and mud stone changes into slate.

2. PHYSICAL CLASSIFICATION

On the basis of physical appearance stones are classified into three main forms namely stratified, unstratified and foliated.

❖ Stratified Rocks: These rocks possess planes of stratification or cleavage. Stratified rocks show distinct layers which can be easily split along these planes. Ex: Sand stones, lime stones, shale, slate etc.

❖ Unstratified Rocks: These rocks possess compact grains and crystalline. These rocks are not stratified and cannot be split into thin layers. Ex: Granite, marble, basalt, etc.

❖ Foliated Rocks: These rocks have a tendency to split up in a distinct direction. In general most of the metamorphic rocks have a foliated structure, whereas quartzite and marble have granulose structure.

3. CHEMICAL CLASSIFICATION

On the basis of chemical characteristics stones are categorized into Silicious, Argillaceous and calcareous rocks.

❖ Silicious Rocks: These rocks are very hard and durable. The primary- constituent is silica (SiO₂). Ex: Granite, sandstones, trap etc.

❖ Argillaceous Rocks: These rocks are hard, durable and brittle in nature. The primary constituent is silica (Al₂O₃). Ex: Slate, laterite etc.

❖ Calcareous Rocks: These rocks are formed from a variety of chemical and detrital sediments. The primary constituent is calcium carbonate (CaCO₂). Ex: Limestone, marble, dolomite etc.