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CHAPTER 6

INVESTIGATION TO PROCURE FRESH SANDSTONE

FOR CONSERVATION AND RESTORATION WORKS

6.1 INTRODUCTION

When obtaining stone for conservation or restoration work, the

ideal situation is to go to the quarries from where the stone was originally

obtained for the construction (Weaver and Matero 1993). But in most of the

cases it is impossible to obtain the stone from the same quarry because the

ancient quarries may not be operational. As for as possible the stone obtained

for the conservation work has to match not only with the nature of the stone

used in the monuments, but also with the colour and texture, so as to merge

with the historic fabric.

This chapter deals with locating compatible fresh sandstone for

future conservation works. The chapter first deals with the identification of

the geographical locations to obtain fresh sandstone in Tamilnadu.

Characterization of fresh sandstone was carried out to understand the nature

of sandstone by detailed megascopic investigation, chemical analysis and

microstructure study. The characteristics of fresh sandstone are then

correlated with the characteristics of weathered sandstone used in the temples

to check the compatibility of the fresh sandstone.

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6.2 IDENTIFICATION OF THE GEOGRAPHICAL

LOCATIONS TO OBTAIN COMPATIBLE SANDSTONE IN

TAMILNADU

6.2.1 Sandstone Exposures in Tamilnadu

The sandstone used in the monuments belongs to the Upper

Gondwana Age (Srinivasan 1971). At present there are no operational

quarries available for sandstone in Tamilnadu. An investigation was carried

out to locate the geographical sites from which compatible sandstone can be

procured for future conservation works.

An examination of the Geological map of Tamilnadu, shows the

distribution of geological formations in the different districts of Tamilnadu

(Figure 6.1). The legend (Blue colour) shows the Lower cretaceous -

Gondwana sediments of sandstone in Tamilnadu, within the boundary of the

Kanchipuram district. This extends into the state of Andhra Pradesh a state

adjacent to Tamilnadu towards the north. This confirms the presence of

sandstone in the entire Kanchipuram taluk and the geological map of

Kanchipuram district supports the historical conjecture that the sandstone

used in the monuments belongs to the Upper Gondwana Age.

6.2.2 Geology of Kanchipuram District

The Stratigraphic succession of geological formations for the

Kanchipuram district is outlined in Table 6.1.

The geological map of Kanchipuram (Figure 6.2) shows the

distribution of the geological formations of different taluks in Kanchipuram

district. The legend (Blue colour) shows the Lower cretaceous -

Gondwana sediments in Kanchipuram Taluk.

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- Upper Gondwana sediments - Charnockite formations - Granite and Gniess formations

Figure 6.1 Geological map of Tamilnadu

Source: Geological Survey of India, 1980

Table 6.1 Stratigraphic succession of geological formations for

Kanchipuram district

(Gazetteers of India, Tamilnadu State, Kanchipuram and

Thiruvallur Districts 2000)

Age Formation Lithography

Recent Alluvium and beach

sands

Sand, gravel, silt and clay

Pleistocene Laterite, soils and talus Laterites, sandy clay and silt

Pleistocene to

Upper Miocene

Conjeevaram gravels Boulders, cobbles, pebbles and

gravels chiefly of quartzite

Lower cretaceous

to Jurassic

Sandstones, shales and

boulder beds

Fine to medium-grained sandstone

with clay intercalations, Big

boulders of granite gneiss with or

with out matrix of clay and sand

Archaean Crystalline formations Mixed gneiss, charnokites, granites

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Figure 6.2 Geological map of Kanchipuram district (part), prepared by

Geological Survey of India, 2003

6.2.2.1 Lithological data of Kanchipuram district

As there are no operational quarries, the lithological report of

Kanchipuram district prepared by the Geological wing, Public Works

Department (PWD), Tamilnadu, was examined confirming the existence of

upper gondwana sandstone in the study area. Lithological report of

Kanchipuram district is presented in Table 6.2.

6.2.2.2 Collection of fresh sandstone samples

A field study was conducted to locate geographical sites to obtain fresh

sandstone based on the lithological data of Kanchipuram district. Five

geographical locations were identified where the monitoring wells are

operated for data collection by PWD, Tamilnadu. Three sandstone samples

were collected from three open wells under the control of the PWD from the

following geographical locations in Kanchipuram taluk. Figures 6.3 to 6.5

show the Topo Map (Part) of Kanchipuram Taluk and Table 6.3 shows the

geographical locations from where fresh sandstone can be obtained in

Kanchipuram taluk, Kanchipuram district.

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Table 6.2 Lithological report of Kanchipuram district (Government of Tamilnadu 2002)

Sl.

No. Well No

Bore

type District Taluk Village

Topo sheet

No Lattitude Longitude Stratigraphy

Station

name Lithology

Monitor

date

Depth in

Meters

1 HP11907 Open

well Kanchipuram Kanchipuram Thiruppakkuzhi 57P/9/SE 12°52'10" 79°37'40" CretaceuTertiary Kanchipuram Clay, clayey, sand sandstone 1/23/2002 7

2 HP11911 Open

well Kanchipuram Kanchipuram Kil Ambi 57P/9/SE 12°51'20" 79°39'20"

Cretaceus

Tertiary Kanchipuram Clay, clayey, sand sandstone 1/23/2002 9

3 HP11917 Open

well Kanchipuram Kanchipuram Mel Ambi 57P/9/SE 12°52'20" 79°38'40" CretaceusTertiary Kanchipuram Clay, clayey, sand sandstone 1/23/2002 9

4 HP11922 Bore

well Kanchipuram Kanchipuram Amaravatipattanam 57P/9/SE 12°52'05" 79°39'40" CretaceusTertiary Kanchipuram

Clay, clayey sand, sandstone

and shales 1/23/2002 14

5 HP11926 Bore

well Kanchipuram Kanchipuram Timmasumudram 57P/9/SE 12°52'10" 79°41'20" CretaceusTertiary Kanchipuram

Sand, clayey sand, sandstone

and conglomerate 1/23/2002 24

Source: Profile of Kanchipuram District- Annexure –II (part) Prepared by Ground and Surface Water Data Centre, Geological wing, Public Works Department, Tamilnadu, 2002.

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Figure 6.3 Topo map (part) of Kanchipuram taluk

Source: Topo sheet No 57P/9/SE, prepared by the Survey of India

Geographical area identified to

procure fresh sandstone

Geographical area where the

sandstone monuments

under study are located

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Figure 6.4 Locations of wells from where fresh sandstone were

procured - Topo map (part) of Kanchipuram taluk

Figure 6.5 Locations of sandstone monuments under study in

Kanchipuram town - Topo map (part) of Kanchipuram

taluk

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Table 6.3 Geographical sites identified from where fresh sandstone

samples were obtained in Kanchipuram taluk

Sl.

No. Taluk Village

Topo

sheet No Lattitude Longitude

Depth

in M

1 Kanchipuram Thiruppakkuzhi 57P/9/SE 12°52'10" 79°37'40" 7

2 Kanchipuram Kil Ambi 57P/9/SE 12°51'20" 79°39'20" 9

3 Kanchipuram Mel Ambi 57P/9/SE 12°52'20" 79°38'40" 9

It was also seen that near the open wells from where fresh

sandstone samples were obtained, important temples are located belonging to

the Pallava period within a radius of 1 Km and these temples are community

promoted temples. As these temples are community temples, they have been

added upon in the early Chola period and they exhibit both Pallava and Early

Chola style. The community promoted temples built with sandstone in

Kanchipuram town are shown in Figure 6.6.

a) Sri Seetheswarar temple b) Satyanatha Swami temple

Figure 6.6 Community promoted temples built with sandstone in

Kanchipuram town

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This negates the conception that royal temples were built largely of

stone and community temples of brick or composite masonry. This also leads

us to redefine that at least in the early stages of the development of South

Indian (Dravidian) temple architecture, a distinction was not made with

respect to the use of material whether the temple complexes were promoted

by the royals or the community. It indicates that temples were built with

materials and resources easily accessible and obtained.

6.3 CHARACTERIZATION OF FRESH SANDSTONE

By means of analytical methods characteristical material properties

of fresh sandstone samples obtained from the field are studied. The analysis

began with the examination of hand samples under the stereomicroscope. The

brownish colour of the fresh sandstone visually matches with the sandstone

used in the temples. Following this preliminary examination, three stone

fragments were selected for thin section preparation and further analysis was

done with a petrographic microscope.

6.3.1 Megascopic Analysis

The megascopic analysis reveals that the rock samples are fresh,

compact and banded. The rock is fine-grained sandstone and brownish in

colour. Carbonate tests (1:1 HCL poured) carried out on the rock samples

show efflorescence which confirms the presence of calcium carbonates.

6.3.1.1 Photographs of the sandstone samples collected from the

wells/field

Figures 6.7 to 6.9 show the photographs of fresh sandstone samples

collected from the field.

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Figure 6.7 Sandstone sample I collected from the site Thiruppakkuzhi

Figure 6.8 Sandstone sample II collected from the site Kil Ambi

Figure 6.9 Sandstone sample III collected from the site Mel Ambi

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6.3.2 Petrological Analysis

6.3.2.1 Preparation of thin sections

Part of the samples was utilized for the preparation of thin sections

and the rest of the samples was used for chemical analysis to find out the

major elements present in the sandstone. Figure 6.10 shows the photograph of

the thin sections prepared from fresh sandstone samples collected from the

field, and Figures 6.11 to 6.13 shows the microphotographs of the samples.

Figure 6.10 Photograph of the thin sections

Figure 6.11 Microphotographs of sample I

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Figure 6.12 Microphotographs of sample II

Figure 6.13 Microphotographs of sample III

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6.3.2.2 Interpretation of the petrological analysis

The microscopic analysis of thin sections of the sandstone samples

revealed the following:

• The sandstone is classified as medium to fine-grained

sandstone. The sandstone is essentially composed of quartz

and feldspar and embedded within the fine ferruginous

matrix. The matrix makes up 10% of the modal content of

the thin section.

• Most of the grains are more angular in nature, larger in size

and indicate very short duration of transportation.

• The large grains are composed of quartz and plagioclase

feldspar.

• Rock shows banding in thin section exhibiting alternate

ferruginous and non-ferruginous layers and uniform in

thickness. The thickness of the band is approximately

2.2mm.

• Pyraxins and opaque oxides are the minor minerals.

6.3.3 Chemical Analysis

The chemical analysis of the fresh sandstone is presented in

Table 6.4.

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Table 6.4 Chemical analysis

Constituents present

in the sandstone

Sample I

%

Sample II

%

Sample III

%

SiO2 39.03 38.42 40.06

Al 2O3 9.65 9.45 9.21

Fe 2O3 3.40 2.93 3.31

FeO 0.50 0.52 0.57

MgO 1.03 1.05 1.10

CaO 17.65 17.50 17.10

Na 2O 2.01 2.05 2.07

K 2O 2.46 2.42 2.35

MnO 0.40 0.35 0.37

TiO2 0.52 0.53 0.59

P 2O5 0.09 0.06 0.05

LOI 16.40 16.05 16.45

6.3.3.1 Interpretation of the chemical analysis

• The analytical results infer that the samples contain 39-40%

silica, 9.2- 9.5% alumina and 2-2.5% of alkalis which

indicate that the samples contain more fine-grained minerals/

clay.

• The calcium content varies from 17-18% which collaborated

with prepositional LOI (16-16.5%). Hence the sandstone is

Calcareous in nature.

• From the silica and calcium content, it is inferred that the

fresh sandstone is Calcareous sandstone with fine-grained

matrix of ferruginous material.

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6.4 COMPATIBILITY OF FRESH SANDSTONE

The sandstone used in the monuments is Calcareous sandstone with

fine-grained matrix of ferruginous material. The sandstone collected from the

field is also calcareous sandstone with fine-grained matrix of ferruginous

material. This confirms the geological compatibility of sandstone used in the

temples and the fresh ones. The megascopic analysis of weathered and fresh

samples reveals that the brownish colour visually matches with the sandstone

used in the temples. Hence the fresh sandstone collected from the field can be

used as a replacement material. The fresh sandstone needs to be tested and

analysed for its engineering properties before it is used as replacement for any

structural member.