Stones

Stones have been used for building purposes from time immemorial. Building stones are obtained from rocks occurring in nature. The different types of rocks are as given below:

Image Credit : Kristina Lindberg

1. Igneous rocks

2. Sedimentary rocks

3. Metamorphic rocks

1. Igneous rocks :

These rocks are of valcanic origin which is resulting of solidification of molten materials. Solidification may have occurred either in the interior of the earth's crust or upon its surface. They represent a crystalline glassy or fused texture. These rocks are hard, tough, dense, impervious, strong and durable. Principal stones obtained from these are granite, basalt, trap and dolerite.

i) Basic rocks :

The igneous rocks containing silica less than 52% are called basic rocks. The color of these rocks is darker than acid rocks. Basalt and dolerite are basic rocks.

ii) Acid rocks :

Igneous rocks containing silica more than 65% are called acid rocks. The rocks are coarsely crystalline and free sillica or quartz can be seen easily. Granite is an acid rock.

2. Sedimentary rocks:

The rocks which are formed from sediments through the agency of water, wind or glacier are called sedimentary rocks. Sedimentary rocks consist of grains of minerals which are cemented together by a binding material which may be calcarious, ferrugenous, sillicious or argillaceous (clay). They usually show the bedded structure arranged in layers. Principal stones obtained from these rocks are sand stone, shale, limestones and laterite. Gravel, sand, silt, clay and peat are considered as uncemented and unconsolidated sedimentary rocks.

3. Metamorphic rocks:

These rocks are the rocks originally formed in either of the above two processes but, subsequently, changed or metamorphosed in colour, structure and texture due to intense heat and pressure below earth's crust. The rocks have a foliated structure in general and also show layers of stratification which are not always uniform. Principal stones obtained from these rocks are quartzite, schist, slate marble and gnelsses.