Basics of building stones

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BASICS OF BUILDING STONES
by
Prof A. BALSUBRAMANIAN
CENTRE FOR ADVANCED STUDIES IN EARTH
SCIENCE
UNIVERSITY OF MYSORE
MYSORE-6

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Introduction:
Stones are naturally occurring rocks of igneous,
sedimentary or metamorphic origin.
Most of the rocks are sufficiently consolidated to
enable them to be cut or made into various shapes
and blocks or slabs to be used walling, paving or
roofing materials. Rocks are mostly used in the
construction of buildings and hundreds of structures.
Stones are categorised into building stones,
ornamental stones and dimension stones.

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A building stone is chosen for its properties of
durability, attractiveness, and economy.
A dimension stone is a building stone that is often
quarried and prepared in blocks according to
specifications. A decorative stone is a stone that can
be quarried, cut or carved and is most highly valued
for its pleasing appearance. It is more often used in
interior construction for decoration and monuments
than as standard building stone.

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Millions of stones of crushed rock are needed
annually for road base, paving, ready-mixed concrete
and asphalt.
The study of the properties of stones is a part of
engineering geology and mining geology.
Geological classification of Rocks:
The geological age of rocks has also some relations
with their properties as building materials.

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As a general rule, the very ancient rocks are more
stronger and more durable, but to this there are many
exceptions.
According to the usual geological classification, rocks
are divided into igneous, metamorphic, and
sedimentary.
The characteristics of various rocks are as follows:

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1) Igneous rocks:
These rocks are formed when the magma from the
earth comes out of the surface or cools inside near the
surface of the earth.
Characteristics:
A. Intrusive - subsurface crystallization
B. Extrusive- above surface crystallization
*note Temperature and time has a lot of effect on
crystal sizes i.e.: Heat + time = Larger crystal.

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Igneous form occurrence below ground presents itself
in 2 basic ways:
Intrusive basic dike, which is like having layers of
cardboard over your head and punching your fist up
into it. Plutonic, this is like a huge hot ball of stone
burning its way around deep below the surface and it
usually has "hot arms" that reach out from its main
mass. Crystal habit can successfully delineate a
Igneous stones origin, usually.

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Dikes are cooler thus forming smaller crystals and
Plutons are hotter thus forming larger crystals.
C. Mineral content
D. Grain size, Plutonic >3/16" coarse. Extrusive 1/64"
- 3/16" Medium and < 1/64" fine
E. Crystal shape
F. Texture % A, %B, crystal angle.
G. Color.

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These rocks are further classified into
A. Acid rocks > 65% Si + > 10% Modal Quartz
B. Intermediate rocks 55% - 65% Si
C. Basic rocks 45% - 55% Si < 10% Modal Quartz
D. Ultra-Basic < 45% Si.

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2) Sedimentary rocks:
Characteristics:
Sandstone, limestone, dolomite originally formed
mainly in sea water, or lakes, from the remains of
animals and plants, also from transportation and
deposition of rock products.

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The uniqueness of these rocks are:
A. Formed at or near the surface
B. Distinctive strata
C. Many fossils have been found in this type of rock
Grain shape
A. Rounded
B. Angular.
These rocks are further classified into :
A. Detrital= is made from disintegrated pre-existing
rock.

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B. Biogenetic= is made from shells and other
fossilized fragments.
C. Chemical= is made from chemical precipitation.
3) Metamorphic rocks:
Metamorphic Rocks form from when pre-existing
rocks are exposed to elevated heat and pressure.
Metamorphism may also deform banding in rocks to
form folded patterns.

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Characteristics:
Marble, serpentine, onyx, slate, quartzite, gneiss are
produced from sedimentary or igneous rocks by the
action of heat and pressure.
The uniqueness of these rocks are:
A. No pressure - fossils survive
B. Low pressure - fossils distorted or destroyed
C. Moderate pressure - Grains form moderately
D. High pressure - Active fluids may circulate
E. Heat alone, Metamorphic Aureole surrounding a
deep plutonic intrusions, possibly with active fluids.

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F. Dynamic Meta - Large scale movement phenomena
G. Crushing actions produce Xylonite Meta rock from
powder
H. Low angle thrust fault: Plate pressure coupled with
subsidence
I. Thrust movement, plate movement
Classification:
1. Structure
A. Contact type is crystalline
B. Regional type is usually foliated

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2. Grain size
A. +0 Big grain, High pressure
B. 00 Med grain, Med pressure
C. -o Small grain, Low pressure
3. Basic PSI and temperature:
Basic PSI and temperature of occurrence is 480* F -
1472* F 2,000 - 10,000 K.

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Parameters in selection of a good construction
stone:
Being cheap, hard, durable and naturally good looking
stones are often used in construction.
There are several properties of stones that are
controlling their types and qualities.
The criteria of selection is based normally on the
following general parameters:
1. Chemical composition of stone

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2. Strength and hardness
3. Durability
4. Resistance to fire
5. Bio-Deterioration
6. Appearance
7. Susceptibility to being quarried in large sizes.
Chemical composition of stones:
Using/selecting a stone for construction, its chemical
properties and composition must be tested and
verified because different elements and compounds in
stones have different properties.

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For instance, Magnesium in Limestone causes it to be
more stronger and is called Dolomite.
Feldspar, in large quantities in stone is a source of
weakness because CO2 dissolves Potassium, Sodium,
and even Calcium in the Feldspar leaving pure white
clay behind.
Presence of Mica, even less than 2-3% makes stone
unsuitable for building purposes. Stones with silicates
as cementing materials are resistant to weathering.

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Factors affecting strength, hardness and
toughness:
a. Hardness or softness of the components
b. Proportions of the hard and soft minerals
c. Size and shape of the minerals
d. Cohesion
e. Porosity
f. Density
g. Cementing material.

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Characteristics of stones:
The following properties of the stones should be
looked into before selecting them for engineering
works:
Appearance:
Appearance is a primary requirement for all stones.
The colour and ability to receive polish are important
factors.

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Bio-deterioration:
Certain trees and creepers thrust their roots into the
joints of stones and have both mechanical and
chemical effects.
Special microbes can grow on the surface and in
minute fissures, their by-products cause flaking and
discoloration.

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Colour:
A stone with uniform and attractive colour is durable,
if grains are compact.
Stones with much iron should be discouraged as the
formation of iron oxides disfigures them and brings
about disintegration.
Marble and granite get very good appearance, when
polished.

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Cost:
Cost is an important consideration in selecting a
building material.
Proximity of the quarry to building site brings down
the cost of transportation and hence the cost of stones
comes down.
However it may be noted that not a single stone can
satisfy all the requirements of a good building stones,
since one requirement may contradict another.
For example, strength and durability requirement
contradicts ease of dressing requirement.

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Hence it is necessary that site engineer looks into the
properties required for the intended work and selects
the stone.
Dressing:
Giving required shape to the stone is called dressing.
It should be easy to dress so that the cost of dressing
is reduced. However the care should be taken so that,
this is not be at the cost of the required strength and
the durability.

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Durability:
Stones selected should be capable of resisting adverse
effects of natural forces like wind, rain and heat.
Ease in Dressing:
Cost of dressing contributes to cost of stone masonry
to a great extent. Dressing is easy in stones with lesser
strength. Hence an engineer should look into
sufficient strength rather than high strength while
selecting stones for building works.

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Hardness:
It is an important property to be considered when
stone is used for flooring and pavement.
Coefficient of hardness is to be found by conducting
test on standard specimen in Dory’s testing machine.
For road works coefficient of hardness should be at
least 17. For building works stones with coefficient
of hardness less than 14 should not be used.

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The stone used in floors and pavements should be
able to resist abrasive forces caused by movement of
men and materials over them.
Percentage wear:
It is measured by attrition test.
It is an important property to be considered in
selecting aggregate for road works and railway
ballast. A good stone should not show wear of more
than 2%.

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Porosity and Absorption:
All stones have pores and hence absorb water. The
reaction of water with material of stone causes
disintegration.
Absorption test is specified as percentage of water
absorbed by the stone when it is immersed under
water for 24 hours. For a good stone it should be as
small as possible and in no case more than 5. Building
stone should not be porous. If it is porous rain water
enters into the pour and reacts with stone and
crumbles it.

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In higher altitudes, the freezing of water in pores
takes place and it results into the disintegration of the
stone. Permissible limits of water absorption for
some the commonly used building stones are as
follow.
Type of
Stone
Maximum limit of
Water Absorption (%)
Sandstone 10
Limestone 10
Granite 1

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Shale 10
Slate 1
Quartzite 3
Resistance to heat or Fire:
Resistance to heat means that the stone must have a
very low amount of expansion due to large increase in
temperature.
Silicious materials are good at areas where resistance
to fire is required.

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Sand stones resist fire better. Argillaceous materials,
though poor in strength, are good in resisting fire.
Seasoning:
The stones obtained from quarry contain moisture in
the pores. Good stones should be free from the quarry
sap. The strength of the stone improves if this
moisture is removed before using the stone. The
process of removing moisture from pores is called
seasoning. The best way of seasoning is to allow it to
the action of nature for 6 to 12 months. This is very
much required in the case of laterite stones.

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Laterite stones should not be used for 6 to 12 months
after quarrying.
hey are allowed to get rid of quarry sap by the action
of nature.
This process of removing quarry sap is called
seasoning.

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Sensitivity to Moisture:
Moisture from rain, snow or other environmental
conditions penetrates the wall leading to cracks,
efflorescence, rust staining, wood rotting, paint
peeling, darkening of masonry and spalling. The
perfect sealing of a masonry wall surface is almost
impossible since fine cracks and joints will allow the
passage of water into the wall.
Some stones have moisture sensitive mineral contents.

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This will cause the stone to develop rust spots, or
other color variations.
The presence of moisture sensitive substances will
cause blotchy and streaking discolorations.
Certain lime stones contain bituminous materials that
are soluble when exposed to moisture. Some marbles
are also moisture sensitive when in high moisture
areas, showers and those with steam features; these
stones have a tendency to develop dark botches.

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Specific Gravity:
Heavier variety of stones should be used for the
construction of dams, retaining walls, docks and
harbours. The specific gravity of good building stone
is between 2.4 and 2.8.
Strength:
Strength is an important property to be looked into
before selecting stone as building block. Indian
standard code recommends, a minimum crushing
strength of 3.5 N/mm2 for any building block.

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Due to non-uniformity of the material, usually a factor
of safety of 10 is used to find the permissible stress in
a stone.
Hence, even laterite can be used safely for a single
storey building, because in such structures expected
load can hardly give a stress of 0.15 N/mm2.
However in stone masonry buildings care should be
taken to check the stresses when the beams
(Concentrated Loads) are placed on laterite wall.

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Structure:
The structure of the stone may be stratified (layered)
or unstratified.
Structured stones should be easily dressed and
suitable for super structure.
Unstratified stones are hard and difficult to dress.
They are preferred for the foundation works.

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Texture:
Fine grained stones with homogeneous distribution
look attractive and hence they are used for carving.
Such stones are usually strong and durable.
Toughness:
Building stones should be tough enough to sustain
stresses developed due to vibrations. The vibrations
may be due to the machinery mounted over them or
due to the loads moving over them.
The stone aggregates used in the road constructions
should be tough.

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The resistance to impact is called toughness.
It is determined by impact test.
Stones with toughness index more than 19 are
preferred for road works.
Toughness indexes 13 to 19 are considered as
medium tough and stones with toughness index less
than 13 are poor stones.

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Weathering:
Weathering is a complex interaction of physical,
chemical and biological processes that can alter the
stone in some general or specific way. The physical
properties of stone differs widely between stone
groups and even within the same stone type.
The mineral composition, textural differences,
varying degrees of hardness and pore/capillary
structure are the main reasons why stone nor all the
surface of the same stone shows signs of alteration the
same and evenly.

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These minerals can be broken down, dissolved or
converted to new minerals by a variety of processes
which are grouped as Mechanical and Chemical.
Intensity and duration are two key elements that
govern to what extent weathering reactions will have
on stone.
Rain and wind cause loss of good appearance of
stones. Hence stones with good weather resistance
should be used for face works.

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Weight and Density:
Building stones must be heavy. Denser stones are
stronger. Light weight stones are weak. Hence stones
with specific gravity less than 2.4 are considered
unsuitable for buildings.
Quality Tests conducted on Stones:
To ascertain the required properties of stones, the
following tests can be conducted:
(i) crushing strength test.

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(ii) water absorption test.
(iii) abrasion test.
(iv) impact test.
(v) acid test.
(i) Crushing Strength Test:
For conducting this test, specimens of size 40 × 40 ×
40 mm are prepared from parent stone. Then the sides
are finely dressed and placed in water for 3 days.

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The saturated specimen is provided with a layer of
plaster of paris on its top and bottom surfaces to get
even surface so that load applied is distributed
uniformly.
Uniform load distribution can be obtained
satisfactorily by providing a pair of 5 mm thick
playwood instead of using plaster of paris layer also.
The specimen so placed in the compression testing
machine is loaded at the rate of 14 N/mm2 per
minute. The crushing load is noted.

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Then crushing strength is equal to the crushing load
divided by the area over which the load is applied. At
least three specimen should be tested and the average
should be taken as crushing strength.
(ii) Water Absorption Test:
Just like a sponge, porous rocks have the ability to
absorb water and other liquids. Water-absorbing rocks
are formed from minerals that can hold water in their
crystal structure or between grain boundaries.

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Such water absorption is often accompanied by a
change in the crystal dimension that manifests itself
as a swelling of the rock. These rocks, including
pumice and sandstone, increase in weight and size as
they take in water.
For the water absorption test, the specimens are dried
in an oven for a specified time and temperature and
then placed in a desiccators to cool. Immediately upon
cooling the specimens are weighed.

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The material is then emerged in water at agreed upon
conditions, often 23°C for 24 hours or until
equilibrium. Water absorption is expressed as increase
in weight percent. Percent Water Absorption = [(Wet
weight - Dry weight)/ Dry weight] x 100 .
(iii) Abrasion Test:
This test is carried out on stones which are used as
aggregates for road construction.
The test result indicate the suitability of stones against
the grinding action under traffic.

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(iv) Impact Test:
The resistance of stones to impact is found by
conducting tests in impacting testing machine .
(v) Acid Test:
This test is normally carried out on sand stones to
check the presence of calcium carbonate, which
weakens the weather resisting quality.

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In this test, a sample of stone weighing about 50 to
100 gm is taken and kept in a solution of one per cent
hydrochloric acid for seven days.
The solution is agitated at intervals.
A good building stone maintains its sharp edges and
keeps its surface intact.
If edges are broken and powder is formed on the
surface, it indicates the presence of calcium
carbonate. Such stones will have poor weather
resistance.

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(vi) Ultrasonic techniques:
Ultrasonic techniques are increasingly being used in
in various fields such as mining, geotechnical, civil,
and underground engineering, since they are non-
destructive and easy to apply. These techniques are
usually employed both in site and laboratory to
characterize and determine the dynamic properties of
rocks.

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Velocity ratio index: An index called a velocity ratio
index (VRI) was defined from ultrasonic
measurements on the stone block and intact rock
specimen.
Common Building Stones:
(i) Granite: Granites are intrusive igneous rocks.
Their colour varies from light gray to pink.
The only natural stones harder than granite are
diamonds, rubies, and sapphires.

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Therefore, choose granite when permanence, enduring
color and texture, and complete freedom from
deterioration and maintenance are prime
requirements.
Granite is highly heat, scratch and stain resistant, and
is commonly used to face commercial and
institutional buildings and monuments.
Commercially, the term ‘granite’ includes a range of
other types of non-granite dimension stone including
any feldspathic crystalline rocks or other igneous or

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metamorphic rocks which possess qualities similar to
granite’s grainy, interlocking texture.
Many variations of granite appear on the commercial
market with white, gray, pink, and red being the most
common primary colors.
The structure is crystalline, fine to coarse grained.
They take polish well.
They are hard durable. The compressive strength is
100 to 250 N/mm2.

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Specific gravity: 2.64 and absorption less than
1%.Crushing strength: 110 to 140 MN/m2
. Colour
depends upon that of feldspar and may be brown/
grey/ green or pink.
Scientifically, an intrusive (plutonic) igneous rock
must contain between 10% and 50% quartz to be
classified as granite, but other similar stones such as
gabbro, diabase, anorthosite, sodalite, gneiss, and
basalt are sometimes sold as “granite” commercially.

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They are used primarily for bridge piers, river walls,
and for dams.
They are used as kerbs and pedestals.
The use of granite for monumental and institutional
buildings is common. Polished granites are used as
table tops, cladding for columns and wall.
They are used as coarse aggregates in concrete.

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Granodiorite:
It is an intermediate intrusive igneous rock
composed of light colored white to light grey feldspar
and dark green to black amphibole and/or biotite. The
mix of light and dark minerals gives the rock a coarse
“salt-and-pepper” appearance.
Gabbro: It is a dark-colored (mafic) intrusive rock
that consists of dark grey feldspar and black to dark
green minerals such as amphibole and pyroxene.

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To a geologist, the term “black granite” would be an
oxymoron, since by definition granite must be light
colored.
(ii) Basalt and Trap: These are extrusive igneous
rocks. The structure is medium to fine grained and
compact. Their colour varies from dark gray to black.
Fractures and joints are common. Crushing strength
is70 to 80 MN/m2
. Specific gravity = 2.96. Basalt is
rough, lightweight and grey to black in colour.

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The compressive strength of basalt varies from 200 to
350 N/mm2. They are used as road metals, aggregates
for concrete. They are also used for rubble masonry
works for bridge piers, river walls and dams. They are
suitable for paving sets and as road metal, for the
manufacture of artificial stones and used as aggregate
in concrete.
(iii) Sand stone: These are sedimentary rocks, and
hence stratified. The stone is composed mainly of
sand-sized grains, or clasts, of quartz cemented with
silica, calcium carbonate, or iron oxide.

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They consist of quartz and feldspar. They are found in
various colours like white, grey, red, buff, brown,
yellow and even dark gray. The specific gravity varies
from 1.85 to 2.7 and compressive strength varies from
20 to 170 N/mm2. Its porosity varies from 5 to 25 per
cent. Weathering of rocks renders it unsuitable as
building stone. It is desirable to use sand stones with
silica cement for heavy structures, if necessary. They
are used for masonry work, for dams, bridge piers and
river walls.

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A range of sandstones exist on the market, varying in
the amount of quartz present in the stone. These
varieties can be different in density, hardness,
porosity, and aesthetics.
The commercial sandstone category encompasses
many variations of texture and color.
Common forms of sandstone include arkose which
has a high feldspar content, graywacke which
contains angular rock fragments, and conglomerate
which contains rounded rock fragments.

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Other common stones included in this category are
bluestone, a hard, dense feldspathic sandstone,
brownstone, a reddish-brown stone taking its color
from its high iron content, and flagstone, a sandstone
or sandy slate that is easily split into large, thin slabs.
(iv) Slate: These are metamorphic rocks. They are
composed of quartz, mica and clay minerals. While
slate is primarily comprised of quartz and either
muscovite or illite, quantities of biotite, chlorite,
hematite, and pyrite are also commonly present.

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Less frequently, apatite, graphite, kaolin, magnetite,
tourmaline, and zircon can be constituents, as well.
The structure is fine grained. They split along the
planes of original bedding easily.
The colour varies from dark gray, greenish gray,
purple gray to black. The specific gravity is 2.6 to 2.7.
Compressive strength varies from 100 to 200 N/mm2.
They are used as roofing tiles, slabs, pavements etc.
Slate is naturally found in an array of colors.

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The most common include black, gray, blue-gray, and
mottled varieties. When iron compounds are present
in the formation, slate can take on hues of brick red,
deep purple, or one of many shades of green.
(v) Laterite: It is a alteration product of a rock. It is
having porous and sponges structure. It contains high
percentage of iron oxide. Its colour may be brownish,
red, yellow, brown and grey. Its specific gravity is
1.85 and compressive strength varies from 1.9 to 2.3
N/mm2. It can be easily quarried in blocks.

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With seasoning it gains strength. When used as
building stone, its outer surface should be plastered.
(vi) Marble: This is a metamorphic rock.
It can take good polish. It is available in different
pleasing colours like white and pink. Its specific
gravity is 2.65 and compressive strength is 70–75 N/
mm2. It is used for facing and ornamental works. It is
used for columns, flooring, steps etc.

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Marble formed from very pure limestone is white, but
the presence of other minerals, as well as clay, silt and
sand, can give it richly varied coloration.
A wide variety of marbles exist on the market, both
foreign and domestic, and these can be drastically
different in density, hardness, porosity, and aesthetics.
(vii) Gneiss: It is a metamorphic rock. It is having
fine to coarse grains. Alternative dark and white
bands are common.

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Light grey, pink, purple, greenish gray and dark grey
coloured varieties are available. These stones are not
preferred because of deleterious constituents present
in it.
They may be used in minor constructions. However
hard varieties may be used for buildings. The specific
gravity varies from 2.5 to 3.0 and crushing strength
varies from 50 to 200 N/mm2.

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(viii) Quartzite: Quartzites are metamorphic rocks.
The structure is fine to coarse grained and often
granular and branded. They are available in different
colours like white, gray, yellowish.
Quartz is the chief constituent with feldspar and mica
in small quantities. The specific gravity varies from
2.55 to 2.65. Crushing strength varies from 50 to 300
N/mm2. They are used as building blocks and slabs.
They are also used as aggregates for concrete.

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(ix) Limestone: Limestone is a sedimentary rock
composed of calcium carbonate, plus calcium and/or
magnesium. It is formed when layers of minerals
(particularly calcite), fine sediment, and the skeletons
and shells of marine organisms undergo lithification.
Terrestrially-formed limestone is known as travertine.
An especially wide variety of limestones exist on the
market, both foreign and domestic, and these can be
drastically different in density, hardness, porosity, and
aesthetics.

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The ability of limestone to readily adapt to various
architectural styles, along with its pleasing natural
color, ease of shaping, and its durability are
advantages that have all worked together to maintain
the stone’s popularity throughout the years.
Common uses of stones:
Stones are used in the following civil engineering
constructions:

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(i) Stone masonry is used for the construction of
foundations, walls, columns and arches.
(ii) Stones are used for flooring.
(iii) Stone slabs are used as damp proof courses,
lintels and even as roofing materials.
(iv) Stones with good appearance are used for the face
works of buildings. Polished marbles and
granite are commonly used for face works.

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(v) Stones are used for paving of roads, footpaths and
open spaces round the buildings.
(vi) Stones are also used in the constructions of piers
and abutments of bridges, dams and retaining walls.
(vii) Crushed stones with graved are used to provide
base course for roads. When mixed with tar
they form finishing coat.
(viii) Crushed stones are used in the following works
also:

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(a) As a basic inert material in concrete mix.
(b) For making artificial stones and building blocks
(c) As railway ballast.
Conclusion:
The dimension, building, and decorative stone
industries today are almost non-existent because of
competition from other, lower cost materials.

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New construction technology, together with a less
labor-intensive economy and modern architectural
leanings have reduced the demand for stone.
While granite, limestone, marble, sandstone, slate and
travertine represent most building stones, there are
countless other options available, such as
agglomerate, cantera, flagstone, onyx, porphyry,
quartzite, semi-precious stones, shellstone, soapstone
and sodalite.

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Throughout history, natural stone has been the
premier building material all over the world.
Natural stone makes homes more sophisticated and
elegant. People perceive it to be high quality and to
have high value.

Basics of building stones

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