Rocks Mining and the Characteristic of Quality Building Stones

Rocks Mining and the Characteristic of Quality Building Stones

Rocks Mining and the Characteristics of Quality Building Stones.' In this comprehensive journey through the geological landscape, we unearth the intricate world of rocks, unveiling their classification, the art of mining, and the indispensable qualities that define superior building stones. From the quarry to the construction site, we navigate through the essential features that make these stones the bedrock of enduring architectural marvels. Join us as we delve into the fascinating realms of geology and construction, discovering the secrets behind these foundational elements of our built environment.

introduction to stone

What is Stone?

Stones are naturally occurring compact, solid and massive materials that make the earth's crust.

• A rock may be defined as the portion of the earth's crust which has no definite shape and structure.
• Almost all rocks have a definite chemical composition and are made up of minerals and organic matter.
• Some of the rock-forming minerals are as follows:
  • a) Quartz
  • b) Feldspar
  • с) Міса
  • d) Dolomite

NOTES

Monomineral rock - Rocks having one mineral. Ex. Gypsum

Polymineral rock - Rocks having more than one minerals. Ex. Granite, Basalt, etc.

• Being aggregation of minerals, the properties of the rocks are dependent upon the character of minerals constituents, identified by their physical properties as follows:

Hardness:

• It is an important property for the rapid determination of minerals.
• It is measured by scratching the minerals with a series of substances of known variation in hardness using the Mohs scale.

Substances	Hardness	scale
Talc	Easily scratched with thumbnail	1
Gypsum	Scratched by thumbnail	2
Calcite	Cannot be scratched by a thumbnail but can be easily scratched by a knife	3
Fluorite	Can be cut by knife with greater difficulty than calcite	4
Apatite	Can be cut with difficulty by a knife	5
Orthoclase	Can be cut with a knife with difficulty on thin edges	6
Quartz	Not scratched by steel, starches glass	7
Topaz	-	8
Corundum	-	9
Diamond	-	10

NOTE

If a given substance is scratched by fluorite and not by calcite, its hardness is between 3 - 4

cleavage:

The measure of the capability of some minerals to split along certain planes parallel to the crystal face.

streak:

It is the mineral's colour in powder form.

Colour:

It is used for metallic minerals but for non-metallic minerals, it is less reliable.

lustre:

It is the shine on the surface of a mineral and its appearance under reflected light.

crystal:

The crystal form is of importance when a mineral tends to develop its natural shape.

classification of rocks

rocks

Geological Classification

A) Igneous Rocks

• Rocks are formed by cooling and solidification of magma or lava.
• These rocks are strong and durable.
• They have crystalline and compact grains.

I) Intrusive Igneous Rocks

• When cooling and crystallization of magma occurs deep inside the earth's surface.
  • a) Plutonic rocks: When magma cools deep inside the earth. Ex. Granite etc.
  • b) Hypabyssal rocks: When magma cools at shallow depth. Ex. Dolerite etc.

II) Extrusive Igneous Rocks

• When cooling and crystallization of lava occurs on top of the earth's surface.
• Ex: Basalt, Trap, etc.

B) Sedimentary Rocks

• These rocks are formed by weathering of pre-existing rocks by external agencies such as wind, air, water, etc.
• These are formed by the consolidation and cementation of sedimentary deposits.
  Example: Sandstone, Gravel, Limestone, Siltstone, Shale, etc.

I) Mechanical (Clastic) Sedimentary Rocks

• These sedimentary rocks are formed due to physical weathering by external agencies such as running water, moving air, thermal effect, acid, etc

II) Chemical Sedimentary Rocks

• These rocks are formed by the chemical action of water, acids, alkalis, etc., on rocks

III) Biological (organic) Sedimentary Rocks

• These rocks are formed by the remains of organisms such as sea animals

C) Metamorphic Rocks

• These rocks are formed from igneous or sedimentary rocks as a result of the action of the earth's movements, temperature and liquid pressure.

Stone	Types	After Metamorphism
Granite	Igneous	Gneiss
Limestone	Sedimentary	Marble
Shale	Sedimentary	Slate
Sandstone	Sedimentary	Quartzite

Physical Classification

chemical Classification

Important question

Q: For the stones given below; granite, sandstone, limestone, marble and slate. Classify them as per their geological, physical and chemical classification.

Sol:

Stone	Geological	Physical	Chemical
Granite	Igneous	Unstratified	Silicious
Sandstone	Sedimentary	Stratified	Silicious
limestone	Sedimentary	Stratified	Calcareous
Marble	Metamorphic	Foliated	Calcareous
Slate	Metamorphic	Foliated	Argillaceous

Rocks Mining and the Characteristic of Quality Building Stones

Stone mining process

A) Quarrying

• The only operation involved in the production of natural stone is termed as quarrying of stone.
• While selecting the quarrying site, the following points must be considered:
  • i) Availability of a sufficient quantity of stone of desired quality. i Proper transportation facilities.
  • iii) Availability of cheap labour and availability of space for the
  • dumping of refuse.
  • iv) Problem of penetration of rainwater.

Quarrying can be done by any of the following methods:

• Excavation Stone buried in the earth or under loose overburden are excavated with chisels, hammers, etc.
• Wedging: This method of quarrying is suitable for soft rocks such as sandstone, limestone, laterite, marble, etc.
• Heating: It is suitable for quarrying small, thin, and regular blocks of stones from rocks, such as granite and gneiss.
• Blasting: Explosives such as blasting powder, blasting cotton, dynamite, etc. are used.

Notes

The blasting powder used in the quarrying process consists of saltpetre (75%), charcoal (15%) and sulphur (10%).

B) Seasoning:

• A freshly cut stone carries some natural moisture known as quarry sap, making it soft and workable.
• The quarry sap is a mineral solution and reacts chemically with the mineral constituents when the stone is exposed to the atmosphere after quarrying.
• The stone becomes harder and more compact after this.
• This process takes about 6-12 months for complete seasoning.
• When the quarry sap evaporates, it leaves a crystalline film on the faces of the stone and makes them weather resistant.
• The dressing before seasoning improves the weather resistance of the stone.

c) Dressing:

• A quarried stone has a rough surface, which is dressed to obtain a definite and regular shape.
• Dressing of stone is done immediately after quarrying and before seasoning to achieve less weight for transportation.
• Dressing of stone provides a pleasant appearance, proper bedding with good mortar joints, special shape for arches, coping, pillars, etc.

Note: Stones obtained from the quarrying process can be used in following activities:

• i) Foundation and wall works
• ii) Facing and architectural items
• iii) Underground structure and bridge
• iv) Heat and chemically resistant items
• v) Road construction items

Important Question

Example 2.2: The preparation of the surface of the stone to obtain plain edges or to obtain stones of required size and shape is known as:
a) Quarrying
b) Seasoning
c) Dressing
d) Blasting

Sol: The preparation of the surface of the stone to obtain plain edges or to obtain stones of the required size and shape is called dressing of stone. So, the correct answer is c).

Note

Position of the natural bed of stone: Natural bed of stone should be perpendicular to the direction of the applied load. In stone arches, stones are placed with their natural beds radial. In walls, stones are placed in such a way that the direction of their natural beds is horizontal. In cornics and string courses, stones are placed with the direction of their natural beds as vertical.

Rocks Mining and the Characteristic of Quality Building Stones

CHARACTERISTICS OF GOOD BUILDING STONE

A good building stone should have the following characteristics:

• a) Appearance: For face work, it should have a fine and compact texture. Light coloured stones are preferred as dark colour is likely to fade away.
• b) Structure: A broken stone should not be dull in appearance and should have a uniform texture free from cavities, cracks and patches.
• c) Strength: A stone should be durable and strong and should have strength between 60-200 N/mm² (crushing strength > 100 MPa).
• d) Weight: It is an indication of the porosity and density. For stability of structure, heavier stones are required whereas, in the case of arches and domes, lightweight stones are required.
• e) Hardness: The hardness is determined by the Mohs scale.
• f) Toughness: The stone used should be tough when vibratory or moving loads are anticipated.
• g) Water absorption: Water absorption should not be more than 5%; if the water absorption is more than 10%, then the stone is rejected.
• Stone should be well seasoned, fire-resistant (it can withstand up to 800°C) and durable.

To understand the concept for CEMENT in building material do visit the following articles