| Types of Stones |
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Natural stones are classified according to their
mineral content and the process of their formation.
Most of these minerals can be identified by their
color, hardness and crystal formation. However, a
wide array of minerals are often difficult to identify.
Many stones look similar to each other, but are actually
different. Good stones are characterized by durability,
hardness, strength, amenability to dressing, appearance,
weight, fineness of grain, compactness, porosity and
absorption.
In order to be suitable as building stones, a rock
should have specific qualities such as capacity to
stand the ravages of time and weather, requisite strength
to bear strain and super-incumbent weight, attractive
colour and general appearance. Its structure must
also be such as to allow quarrying into good sized
blocks or planes. India possesses extensive deposits
of different kinds of building and monumental stones.
It is one of the few major countries known for the
production and export of natural building stones of
various colours. The most important building stones
in India are the granites/and allied rocks, sandstone,
limestone, slate and marble. The different types
of stones are:
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I. Sedimentary Stones
These stones came from organic elements such as glaciers,
rivers, oceans, and plants. Tiny sedimentary pieces
broke off form these elements and accumulated to form
rock beds. They were bonded through millions of years
of heat and pressure. Major types of sedimentary stones
are:
Limestone
Mainly consisting of calcite, it does not show much
graining or crystalline structure. It has a smooth granular
surface and varies in hardness. Some dense limestone
can be polished and is more likely to stain than marble.
Common colors are black, grey, white, yellow or brown.
Limestone is known to contain lime from sea water, and
that's why the nomenclature.
Sandstone
Sandstone is a sedimentary stone that is typically the
result of quartzite stone being eroded and redeposited
by either wind or water. Sandstone mostly consists of
quartz, silica, iron oxide and calcium carbonate and
are durable, weather, acid and thermal resistant and
have crushing strength. Sandstones are most highly craftable
and manageable, they can at most take a honed polish,
and are used as garden and commercial landscapes, exterior
wall claddings, panels, pillars, sculptures, arches,etc.
They come in an array of colors & shades and can be
chiseled and dressed to a smooth surface in various
attractive shapes.
Soapstone
It is a very soft stone made of a variety of talc. It
is a dense mineral that wears well and is often resistant
to oxide.
Travertine
Usually it has a cream or reddish color and is formed
through the accumulation of calcite from hot springs.
It contains lots of holes that were formed from water
flowing through the stone. These holes are often filled
with synthetic resins or cements and requires lots of
maintenance if the holes are not filled.
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II.
Metamorphic Stones
These stones originates as a result of natural change
from one type of stone to another type by the mixed
action of heat, pressure and minerals. The change may
be a development of a crystalline formation, a texture
change, or a color change.
Marble
The term "Marble" is derived from the Latin
word "Marmar" which itself comes from the
Greek root "Marmarous" meaning thereby a shining
stone. Marble is a metamorphic rock resulting from the
re-crystallization of limestone softened from heat and
pressure. Main constituents are calcium and dolomite.
Hardness ranges from 2.5 to 5 on the MOH scale. Marble
is usually heavily veined and shows lots of grains.
Dimensional marble specifications include smooth textures,
ease in crafting sculptures, hence highly manageable.
It is a reasonably strong and durable stone. It takes
good polish, popularly used as wall claddings, floors,
skirtings, table tops, treads and risers, sculptures,
artifacts, et c. Marble is classified into three
categories:
- Dolomite: If it has more than 40% magnesium
carbonate.
- Magnesium: If it has between 5% and 40%
magnesium.
- Calcite: If it has less than 5% magnesium
carbonate.
Slate
Slate is a very fine grained metamorphic rock derived
from the sedimentary rock 'shale'. Slate is composed
mostly of mica, chlorite and quartz. Characteristically,
the rock may slit into relatively thinner slabs and
can break easily. Some slates take very good polish,
are extremely beautiful and more cost effective than
most other wall and floor coverings. Slate has a fine
to medium grained surface texture. It renders a very
graceful, natural finish to any building or home.
Serpentine
It is identified by its marks, which look like the skin
of a serpent. Hardness rates from 2.5 to 4 on the MOH
scale and most popular colors are green and brown. Contains
lots of magnesium, and has an igneous origin. It does
not always react well to recrystallization or diamond
polishing.
III.
Igneous Stones
These rocks are mainly formed through volcanic material
such as magma. Underneath the earth's surface, liquid
magma cooled and solidified. Mineral gases and liquids
penetrated into the stone and created new crystalline
formations with various colors.
Granite
The term "Granite" is derived from the Latin
word "Granum" meaning "grain" because
of its granular nature. Granite is an Igneous Stone,
primarily made of Quartz(35%), Feldspar(45%) & Potassium.
Dimensional granite specifications include high load
bearing capacity, amenability to cutting without secondary
flaws, ability to yield thin and large slabs and - above
all - durability. Granite is a very strong and durable
stone. It takes heavy gloss polish, popularly used as
architectural stone for interior and exterior walls,
floors and monumental stone.
IV.
Man Made Stones
These stones are derived from unnatural mixtures such
resin or cement with the additive of stone chips.
Terrazzo
Marble and granite chips embedded in a cement composition.
Agglomerates
or Conglomerates
Marble chips embedded in a colored resin composition.
Cultured
or Faux Marble
It is a mix of resins that are painted or mixed with
a paint to look like marble.
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