What is STONE? Uses, Properties, Characteristics of stones, etc.

Stone is a  natural material of construction. It is obtained by disintegration rocks. The stone which is used for construction of engineering structure, is called building stone. Building stone should possess enough strength and durability. It is being used as construction material from very early times.

In this blog, we shall deal with its classifications, properties, uses, etc.

USES OF STONE

• In building construction work, it is used in masonry work, construction of walls, foundations, lintels, damp proof courses, coping, cornices, etc.
• Facial work - It is used as cladding or facing of the building to meet appearance and ornamental requirements.
• Heavy engineering works - It is used in construction of bridges, piers and abutments, gravity dams, retaining walls, etc.
• Stone is used as roofing and flooring material of a building.
• Stone is used as road metal.
• Stone is used as ballast in permanent way of railway tracks.
• Stones are used in manufacture of cement. 
• It is used in making water baths, urinals, electrical switchboards and other products.
• It is used in water treatment process.
• It is used as an aggregate (coarse) in concrete.

CLASSIFICATION OF ROCKS

As the stones are obtained by breaking natural rocks, the type and nature of rocks determine the quality and property of building stone.

Geological Classification

These are of three types :-

(i) Igneous Rocks : These are formed by cooling of molten lava outside or inside the surface of the earth during volcanic eruptions. The molten rock is called magma which on solidification becomes igneous rock.
Example - Granite (intrusive igneous rock), Basalt (extrusive igneous rock), Trap etc.

(ii) Sedimentary Rocks: The rocks formed by gradual deposition (consolidation of particles of the preexisting rocks under the effect of weathering agencies such as running water, wind, glacier etc. are called sedimentary rocks.
Examples - Sandstone, limestone, conglomerate.

(iii) Metamorphic Rocks: These rocks are formed from igneous or sedimentary rocks under the influence of heat and pressure.
Examples - Marble, slate, gneiss etc.

Physical Classification

These are of two types :-

(i) Stratified Rocks: Theses rocks can be split into thin sheets.
Examples - Sandstone, Limestone, Slate etc.

(ii) Unstratified Rocks: These rocks can't be split into thin sheets. It does not have Layered structure.
Examples - Marble, Granite, Trap etc.

Chemical Classification

There are three types in this category :-

(i) Calcareous Rocks: These rocks have calcium carbonate as their chief constituent.
Examples - Marble, Limestone etc.

(ii) Argillaceous Rocks: These rocks have clay or alumina as their chief constituent.
Examples - Slate, Laterite etc.

(iii) Siliceous Rocks: These rocks have silica as their chief constituent.
Examples - Sandstone, Granite, Trap etc.

QUALITIES/CHARACTERISTICS OF A GOOD BUILDING STONE

A good building stone must possess the following characteristics :

Appearance: It should have a uniform and pleasant colour without any cracks and patches.

Hardness/ Toughness: A good building stone should be able to resist abrasive forces (wear and tear) and vibrations of moving loads.

Strength : It should be able to withstand compressive stresses. In general, its crushing strength should not be less than 1000 kg/cm2.

Durability: A good building stone must be durable enough to resist effects of atmospheric/weathering agencies. Examples: rain, wind, temperature etc.

Texture : A good building stone should have compact and crystalline structure.

Porosity/Absorption : A good building stone should not be porous and not absorb more than 5% of water.

Specific Gravity/ Heaviness : The stone to be used in heavy engineering works, docks, and dam must have high specific gravity. In general, it varies from 2.4 - 2.8.

Workability : It should be easy to dress into definite shape for carving and structural work.

Resistance to fire/electricity : It should be able to resist high temperature and offer good resistance to electricity.

Cost : It should have low quarrying cost, dressing cost and transportation cost.

PROPERTIES & USES OF COMMON BUILDING STONES

Granite

This is a common variety of igneous rock formed by cooling of magma below the earth surface. Its properties and uses are as follows:

Properties :-

• Specific gravity - 2.6 to 2.7 
• Unit weight – 2640 kg/m³ 
• Compressive strength - 770 - 1300 kg/cm² 
• Fine grained and can be polished.
• Available in variety of colours and shades - Grey, pink and black.
• Hard, very strong, durable, less workable, less porous, not fire proof and costly to dress.

Uses :-
Suitable for heavy engineering works like bridges, dams, harbours, piers, railway ballast, aggregate in concrete, road metal, column of the building, decorative and monumental works.

Basalt and Trap

These stones are the common varieties of igneous rocks (extrusive type) which are formed by cooling of 'magma' on the earth's surface.

Properties :-

• Specific Gravity - Basalt - 2.80, Trap -2.95
• Unit weight - 2900 kg/m³
• Compressive strength/crushing strength  -  1530 to 1890 kg/cm² for basalt and 3300 to 3800 kg/cm² for trap.
• Dark in colour & shade like black, blue & greenish grey.
• Very strong, hard & tough, less workable, durable, less porous.

Uses :-
Used for floor slabs, foundations, road paving, railway ballast, aggregate in concrete, road metal etc.

Sandstone

It is a common variety of sedimentary rocks, stratified and siliceous in nature.

Properties :-

• Specific gravity  - 2.3 - 2.95
• Unit weight - 2170 - 2350 kg/m³
• Crushing strength - 400 - 650 kg/cm²
• White, grey, brown, red in colour.
• Not very hard, more porous, easy to work and fire resistant (upto 800°C).

Uses :-
Suitable for stone masonry, construction work of architectural importance heavy engineering works, monumental buildings, dams, docks ete.

Limestone

It is a common variety of sedimentary rocks of chemical origin. It is chiefly composed of calcium carbonate with no traces of impurities.

Properties :-

• Specific gravity - 2.5 
• Unit weight - 1720 - 2500 kg/m³
• Crushing strength/Compressive strength - 550 kg/cm
• Available in white, gray, brown and black color.
• Compact variety is hard strong and durable.
• Easy to work with fire resistance up to 900°C with water absorption (up to 4%).

Uses :-

• Used for manufacture of cement and lime, masonry (interior) walls, and paving streets.
• Used in large quantities in blast furnaces bleaching, tanning etc.
• Not fit for use in areas exposed to acidic fumes and smoke.

Marble

It is a most common variety of metamorphic rock. It is a stratified and calcareous. It is chiefly composed of calcium carbonate.

Properties :-

• Specific gravity - 2.65 to 2.72 
• Unit weight - 2700 kg/m³
• Crushing strength - 700 kg/cm²
• Color - White, gray, black, pink, brown, yellow and combination of these.
• Less durable, easily workable (carvable).
• Can take fine polish because of being compact and crystalline in structure.
• Its water absorption is 1-3%.

Uses :-

• Mainly used for ornamental works and superior/specialized building works.
• Can be used in columns, flooring, staircase steps etc.
• Also used for electrical switchboards, wall lining and other decorative purposes.
• Can be used for making floors and facing works, columns or ornamental works.