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Importance of Geology in Rock Monuments
 

Importance of Geology in Rock Monuments

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    Importance of Geology in Rock Monuments Importance of Geology in Rock Monuments Document Transcript

    • Importance of Geology in Rock Monuments Dr Vadagbalkar S.K. Page 1 Importance of Geology in Rock Monuments Abstract: The Indian monuments are the living examples which take us back to thousands of years and helps in exploring the history of India. These monuments- dominated by Megalithic structures - which are in large stone that has been used to construct a structure or monument, either alone or together with other stones, utilizing an interlocking system without the use of mortar or cement. Rocks that can stand the ravages of time and weather, those that possess the requisite strength, homogeneous - or monolithic nature, compact- hard with fine grains, an attractive colour and appearance, and most important is their dressing character, are the most valuable factors considered in the past for selection of construction and carvings of archaeological monuments and structures. Combined with natural hazards, weathering process, climate conditions, and topography etc. has either destroyed completely or left these monuments as partial ruins. Keywords- Carvings, Geological weathering, Megalithic, Stone Monument -------------------------------------------------------------------------------------------------------- Introduction: The earliest phase of Indian architecture may be seen from the remains of the ancient cities of the Indus Valley culture datable to c. 3000 B.C. Materials for sculpture can be just stone, bronze, clay and durable wood in case of India. Most of these materials are long lasting materials. It is based on the fact, the varieties that was available in plenty of manner in particular region was used for the art. Metal used can be ranged as per the quality and resistance. There is no doubt that the purpose of creating sculpture has been to create a piece of art that should be permanent as far as possible. Therefore, with that aim the work was usually produced in durable and frequently expensive materials, primarily Bronze. Very rarely precious materials such as gold, silver, jade and ivory were used for preparing art works. But more common, mostly preferred and less expensive materials that was used for producing sculpture on wider scale are stone & wood. The architecture of the Asokan period (c. 273-237 B.C.) gains in magnificence, as for the first time stone was employed instead of wood. The general sequence is as follows: 1) Harappan culture`s sculpture was made mainly from clay material, probably due to easy availability in surrounding( agriculture man) and understanding its casting- molding capacity. 2) Then there was a boom of creating wooden sculpture. People were used it for houses and in the temples. Examples are the statue of Sun in Multan, statue of
    • Importance of Geology in Rock Monuments Dr Vadagbalkar S.K. Page 2 Lord Jagdish in Jaganathpuri and Rannadevi`s statue in the Mahalaxmi temple of Patan in India. 3) Followed with time, the Car-vary shifted to softer rock material like soapstone, steatite (Talc), slates and Marbles. In Gujarat and Rajasthan, carving on red and white stone and on marble is found in the form of statues. 4) But the sculpture on the hard and massive, largely monolithic stones found its presence at great extent in the history of sculpture. Stone sculpture is found generally in hilly, rocky areas mainly in form of the caves. Perhaps no branch of human culture reflects with greater exactitude the progress or decadence of man than architecture. The progress of Indian architecture from the primitive to the sophisticated is example of progressive historical process. In geologic time and with the progressive growth of human race and culture the earth material available in surrounding and/or nearby were mainly used for living and protection. In the development of architecture, from the most primitive types of human habitation and settlements to magnificent temples and palaces, we can detect the aesthetic taste which actuated man to combine beauty with utility and his ceaseless efforts to express his social and religious environment and his attitude towards life. India is among one of the rare and unique countries in the world which stands for its ancient cultures and traditions, which range through a span of centuries. It is clearly evident from the remains of the ancient monuments and traces in the different parts of India. The Indian monuments are the living examples which take us back to thousands of years and helps in exploring the history of India. These monuments- dominated by Megalithic structures - which are in large stone that has been used to construct a structure or monument, either alone or together with other stones, utilizing an interlocking system without the use of mortar or cement. The construction of these structures took place mainly in the Neolithic and continued into the Chalcolithic and Bronze Age, in India offers a great help to study and know more about the ancient civilizations of India. In accordance with the Geology of India, the development of art and architecture in India has taken place which is reflected in form of magnificent structures either individually or in collective groups. The continuation (extension), renovation and newer design adaption in some structures also tells us about the reviewing attitude of the constructors along with the conservation and protection of these monuments. However with the passage of time and changing political scenario, Iconoclasm, passive mind set towards national properties, non-maintenance etc. sometimes combined with natural hazards, weathering process, climate conditions, and topography etc. has either destroyed completely or left these monuments as partial ruins. Whatever is left behind is our pride and national heritage. Protection, reconstruction or renovation by maintaining the originality of such monuments and their conservation is a policy of our Indian Government which is implemented through
    • Importance of Geology in Rock Monuments Dr Vadagbalkar S.K. Page 3 Archaeological Department. In this context, Geo-archaeological knowledge is essential. Natural stone, similar to other nature-derived materials, can be highly prone to deterioration, both due to improper use and or deterioration in the quality of the environment to which it is exposed. This is followed by loss of its integrity and function. The knowledge of stone properties, their development through time and under weathering conditions therefore constitutes a crucial part of natural stone research. Although highly durable when properly applied, no stone type can be considered immortal (Schaffer 1932) and most of the stone varieties are affected by a polluted atmosphere (Winkler 1997). Deteriorated stone on monuments should be preferably replaced by stone varieties of the same composition from the same quarries. However, this is often not possible, and so stone having similar properties and appearance must be sourced (Prˇikryl 2007). The main aim of this research is to seek compatible stones in terms of appearance and geochemical-physical properties. This task requires a thorough understanding of both the rock properties and its response to external conditions and weathering agents. Weathering Characteristics: Climate, which is usually measured in terms of temperature and moisture, can drastically affect the rate and type of weathering. In an area with cold temperature, for instance, frost wedging would be the dominant form of physical weathering. Chemical weathering occurs most rapidly in a high temperature climate. Though Weathering is a slow process, rock that is exposed to the atmosphere tends to weather much quicker. Mineral composition is also affected by physical weathering a natural process of physical disintegration of a rock into smaller fragments, each with the same properties as the original (without changing the chemical composition), under the effect of mainly by variations in temperature and pressure. The basic types include Frost action (in cold climate area), Abrasion (action by running water), Exfoliation- Surface fracturing (effect of release of pressure), Minerals that are soft (hardness lower than six) can be easily abraded and worn down. All chemical and physical properties are determined by the mineral composition of the rock. Mineral composition is more important in determining the rate of chemical weathering- process by which the internal structure of a mineral is altered by the addition or removal of elements. Change in phase (mineral type) and composition are due to the action of chemical agents. Chemical weathering is dependent on available surface for reaction temperature and presence of chemically active fluids. Smaller particle sizes weather by chemical means more rapidly than large particles due to an increase of surface area. Those minerals that are most reactive with acids, water, and air are weathered at a more rapid rate e.g. calcite (calcareous-
    • Importance of Geology in Rock Monuments Dr Vadagbalkar S.K. Page 4 carbonate matter) in Marbles, limestone, Basalts etc., Feldspars in Granite, Gneiss and Sandstones. The general pattern of weathering can be compared with the chart given below, for any region. Stone/Rock Properties and Sculpturing: All stone can be identified by the chemical composition of the mineral (a pure, solid crystalline substance) or the combination of minerals and non-crystalline substances of which it is made up. The study of rocks is based on a science that uses many properties for identification and classification. Understanding these properties will not only help sculptors understand the materials they are using, but will help them in the selection and carving of stone. Not all properties are relevant to sculptors; those that are useful are described in detail here: Hardness-This describes a stones ability to resist abrasion or scratching, or the ability of one substance to scratch another. Geologists use the Moh's Hardness Scale based on 10 minerals as an arbitrary way to test this property: H-1 Talc, H-2 Gypsum, H-3 Calcite, H-4 Fluorite, H-5 Apatite, H-6 Orthoclase, H-7 Quartz, - (Hardness 1 to 7 is common range of Normal Rock forming Minerals used for construction) H-8 Topaz, H- 9 Corundum, H-10 Diamond,- (Hardness 8 to 10 is common range of minerals used as Gem or Precious/Ornamental stones) The rocks with minerals that can be scratched by a fingernail (H- 2.5) are called "very soft", and those that can be scratched by a copper penny (H- 3.5) are called "soft".( e.g. Marble, Soapstone, Slate) Those that can be scratched by a pocket knife (H- 5.5) are called "semi-hard"(e.g. Schist, Limestone, Vesicular basalt) and those that cannot be scratched by a pocketknife(H- 6- 7) "hard"(e.g. Massive Basalt, Sandstone) and Weathering Regions
    • Importance of Geology in Rock Monuments Dr Vadagbalkar S.K. Page 5 those that cannot be scratched by a steel file(H-7) are called "very hard" (e.g. Granite, Charnockite, Gneiss, Quartzite) Toughness and Brittleness- These properties are often confused with the hardness of a mineral. A "fragile" mineral is one that is easily split or broken into pieces. The term "brittleness" is another term that is applied to a mineral that rather than pulverize tends to shatter. This could be a soft mineral such as a piece of Talc (hardness = 1) or it could be a piece of Quartz (hardness = 7). A piece of Jade, on the other hand although having a hardness less than or equal to a piece of glass may not break even when hit with a hammer. The term for this is called "toughness". A stone that is not brittle is often difficult to split when driving a wedge or chisel into the stone. Rather than allowing the tool to drive into the stone to split it apart, these stones will tend to pulverize around the tool leaving just small chips and powder. The quality of brittleness is also important when carving. When carving a brittle stone it may be easier to crack or shatter the stone if hit too hard. Alternatively a stone that is not brittle that is hit too hard will crush that section of the stone leaving what is called a "bruise". Bruises must be eliminated by carving or sanding deeper to remove it, or will show up on the finished piece. The effect of bruising or leaving tool marks in a stone is also an effective way to contrast one area of the sculpture with another area that is highly polished. This technique is often called "texturing" the stone e.g. Fine grained, compact and massive - Sandstone, Granite, Charnockite, Basalt and Marble. This is another indicator of how a stone breaks, also described using the term "layering" or "grain". Those minerals with a strong layering will break in a predictable manner, called cleavage or weak planes, giving a generally flat plane according to the crystal structure. Although many stones do not have strong cleavage almost all will exhibit some of this property on close inspection. The surfaces of those that do not break in a predictable manner are called fracture. Some brittle stones fracture in with patterns of curved ripples similar to the pattern and shape of a clam shell. This phenomenon is called conchoidal fracturing. Cleavages and/or fracture in rocks affect the shaping-crafting in them. In many monumental sculptures, due to such characters, non-uniformity, damages and asymmetry is observed, especially where they are hewn in Schist, weak foliated Gneisses, Shale, vesicular / amygdaloidal Basalts, Limestone, Quartzite and Marbles. Density - The density of a stone is typically measured as the mass of a stone per unit of volume (grams per cubic centimeter), known as the specific gravity. The specific gravity measures how many more times the stone will weigh compared to an equal volume of water which weighs 1 gram per cubic cm or one thousand kg per cubic meter- e.g. a mineral with a specific gravity of 5 will have 5 times the weight of a similar volume of water. A very light mineral will have a specific gravity that is less than 2, and a heavy mineral will have a specific gravity greater than 10.
    • Importance of Geology in Rock Monuments Dr Vadagbalkar S.K. Page 6 For a sculptor a more commonly used measure of the density is pounds per cubic foot, of which water weighs about 62.5 pounds. Some examples of common stones are: Calcite (Marble) SG = 2.71 (170 pounds) Gypsum (Alabaster) SG = 2.35 (147 pounds) Colour - Some pure minerals occur mainly in one distinctive color, others may occur in many different colors. For the purpose of sculpture the purity of stone is not really a factor but it is attractiveness and further assuming that the impurities do not affect the ability of the stone to be carved. Because most stones are often a mixture of minerals, it is possible to find the same types of stone in a never ending variety of colors and patterns. A stone that is durable, heavy , attractive coloured, fine grained, compact and massive which can be cut or finished accurately to definite shape and size; thick- bedded, evenly grained rock which can be easily cut in any direction and dressed for masonry; is generally considered as the favourable stone for art and architecture. Replacement of once deteriorated parts of stone construction raises important issues concerning the compatibility of fresh versus weathered and or original versus new (alien) stone varieties. The restoration of monuments also requires solid knowledge on the past resources that have ceased to be available over the past century. Indian Geological Setting: Geology of India is as diverse as its geography and people. It contains rocks covering almost the entire spectrum of the Geological Time Scale – ranging from present to past about 3800 million years. 1) The Archeans:- Dharwar and Peninsular Complex - The term Archean refers to fundamental and very ancient complex unit of rocks like Gneisses, Schists, Granulites and Granites which constitutes the basement platform on which all younger sedimentary and volcanic formations rest. As these rocks are crystalline Igneous and/or re crystalline Metamorphic, are generally hard, compact and massive in nature. With the geological time and natural wear and tear the Schists and Gneisses-which have banded or parallel elongated mineral orientations - when exposed on surface disintegrate and decompose faster than Granites and granulites- which have fine grained rounded minerals. Marbles and Schists are relatively softer than other rocks. In India Archeans are found in abundance and cover nearly 2/3rd of the Peninsular India. i.e. they are very well exposed in larger parts of South-India- Karnataka, Andhra Pradesh, Tamilnadu and Kerala, Aravallies in Rajasthan, some parts of Madhya Pradesh, Maharashtra, Goa, Singhbhum and adjoining parts in Bihar, Orissa and Eastern-Ghats ranges. Granites, Charnockites and massive Gneiss forms very durable monumental and ornamental stone. These are compact with homogenous grain nature. Having wide range in appearance and colour- white, pink, red, grey, black etc., are found used
    • Importance of Geology in Rock Monuments Dr Vadagbalkar S.K. Page 7 widely in ancient temples and palaces in South India, which stand today almost intact after centuries of wear. The Marbles of crystalline nature with beautiful white colour mainly comes from Aravalli- Rajasthan – in which famous Taj Mahal is built, along with coloured varieties from surrounding areas, used as ornamental and decorative stone. Due to relatively soft nature (hardness 3) combined with fine grained, homogeneity and massiveness these are widely used. These get fine polish and delicate carvings and sometimes even transparency. The accessibility of this stone nearby gave stimulus to Moghul taste for architecture in the seventeenth century. However with the passage of time on exposure to rains, moisture, snow, micro plants growth on surface, due to variations in temperature, climate, atmosphere either naturally or artificially can bring out drastic changes in appearance, and durability (strength) of rocks. 2) Cuddapah Super group: - The name of this system has been derived from the Cuddapah basin of Andhra Pradesh where they are well exposed .It mainly includes marine sediments, which are metamorphosed from lower to medium grade i.e. meta sediments as Quartzite, Slates, Phyllites intercalated with Shale in layers and Marbles. Equivalents of Cuddapahs are mainly found in parts of Delhi, Rajasthan in some parts of Vidarbha and Kolhapur in Maharashtra and Karnataka. 3) Vindhyan Super group: - The Vindhyan constitutes mainly un-metamorphosed marine sedimentary rock layers of Limestone, Sandstones and Shales. The Vindhyan rocks are mainly well exposed in parts of Madhya Pradesh and their equivalents in certain parts of Andhra Pradesh and Karnataka. Massive varieties of different colored lime stones were mainly used as decorative stones. Lime stones were mainly used in preparation of lime (by burning) to use as binding material, to strengthen the structures. Normally in dry climate lime stones are hard stones, but in acidic environment and heavy rains, they decompose easily. Bedded and massive varieties of Sandstones have proved their importance in building of huge structures like forts, palaces, temples, buildings etc. Especially fine to medium grained and compact varieties have been used for sculpturing. Coarse grained varieties are found susceptible for weathering and erosion, hence were not used for delicate works. 4) Gondwana Super group: - The name of this formation is derived from the Gond – then kingdom in Madhya Pradesh. The Gondwana rocks are mainly fresh water sediment layers in form of sand, silt and clay mixed with coal beds are found deposited in shallow, elongated basin brought about by block faulting. The Gondwana rocks are distributed in parts of West Bengal, Bihar, Madhya Pradesh, Maharashtra and Orissa states-seen well exposed in Damodar and Son valley, Upper Narmada and Godavari valley and Mahanadi valley.
    • Importance of Geology in Rock Monuments Dr Vadagbalkar S.K. Page 8 5) Deccan Trap: - The Deccan Trap is one of the largest volcanic igneous province exposures on land in peninsular India, covering nearly 80% of state of Maharashtra and adjoining parts in Madhya Pradesh, Gujarat, Andhra Pradesh and Karnataka. It consists of multiple layers of solidified flood basaltic rocks. The Ajanta caves have been cut into the 200 m-thick Deccan trap basalts. The thickness of individual flow varies from 1.5 m to 30 m. The various types of traps recognised in the caves are: 1. Vesicular (a) hard vesicular with or without amygdales-porphyritic/non-porphyritic. (b) Soft vesicular with or without amygdales – porphyritic / non-porphyritic. 2. Massive (a) coarse-trap- porphyritic / non-porphyritic (b) fine trap-porphyritic/non-porphyritic Though a pick-axe was used initially for the excavation, the finishing and carving were done mostly by hammer and chisel. The entire works of quarrying of stones, dressing and finishing were done simultaneously with great care and precision. From the methods of excavation and support followed it seems likely that the ancient builders had sufficient knowledge of the principle of single and multiple beams and cantilever system for distributing the loads. Examples of Natural damages: (In Maharashtra) 1) A beautiful little island, named Elephanta, located about 11 km off Bombay is famous not only for its picturesque surrounding but also for its treasure of sculptures in a rock-cut cave temple was built around the same period or a little later (850 A.D.) as the Ellora temple. It has the same style of architecture as that of the Kailasa temple of Ellora, representing the latest phase of rock-cut architectural activity in India. The Elephanta cave is a Siva shrine. The beautifully carved columns of the hall and the entrance have square sections at the basal part that become circular with bas-relief ended with apsidal towards the top. The Elephanta cave, like Ajanta and Ellora, has been carved out in the Deccan trap basalt, and the carvings are mostly in soft vesicular type of flow layers. Removal of the zeolite from the vesicles by the natural processes has given pitted appearance to many of the carvings. Weathering along the flow junction and joint planes in the rock, are responsible for damaging parts of the temple walls or columns as well as for the mutilation of the carvings. 2) Ajanta and Ellora Caves in Maharashtra, India often and has been deeply influenced by these 2000-year-old caves. In these caves, Hindu and Buddhist monks have painted and carved on the stone walls for decorative as well as record purposes. Most of these caves have not been maintained well and the passage of time is clearly marked on the beautiful art. Ellora Caves Paintings and Sculptures Damaged by Rainwater. The ancient Ellora caves in Aurangabad city, India were constructed between the fifth and tenth centuries AD by Hindu, Buddhist and Jain monks. Now the sculptures and famous paintings in the caves are starting to lose
    • Importance of Geology in Rock Monuments Dr Vadagbalkar S.K. Page 9 their gleam, due to rainwater seepage. It is the largest monolithic structure in the world, carved top-down from a single rock. It contains the largest cantilevered rock ceiling in the world. The Ellora rock-cut caves, the most spectacular of India's monuments, are located 29 km northwest of Aurangabad. The majestic beauty, the architectural style and the sculptures carved out of the Deccan trap rocks of Ellora have been acclaimed by the entire world. The excavations were executed in different periods. The contruction was started in 2.5 century A.D. and was continued later in the 5th and 6th centuries A.D. in the Buddhist style of architecture. The construction activity,between 6th and 9th century A.D. was continued, mostly by the Hindus and Jains. Author: - Dr. Vadagbalkar S.K. Head and Associate professor in Geology D.B.F. Dayanand College of Arts and Science, Solapur- Maharashtra State Email: vadagbalkar@gmail.com ------------------------------------------------------------------------------------------------------- Bibliography: Currier, L. W. (1960). Geological appraisal of dimension- stone deposits; Geological Survey Bulletin; 1109, 1–78 Krishnan, M.S.(1982). Geology of India and Burma.(6th Ed.). CBS Publishers;. India, 536p Pascoe, E.H. (1973). A manual of Geology and Burma, Geological Survey of India, Publication, 485p PRˇIKRYL,R. (2007). Understanding the earth scientist’s role in the pre-restoration research of monuments: an over-view;. In : PRˇIKRYL, R. & SMITH, B. J. (eds) Building Stone Decay: From Diagnosis to Conservation. Geological Society, London, Special Publications, 271, 9–21. Schaffer, R.J. (1932). The Weathering of Natural Building Stones; Donhead facsimilie, 2004 The Monuments of India, First Online: May 27, 2000. Wadia, D.N.(1976). Geology of India (4th Ed.);.Tata-McGraw-Hill Publ.co, New Delhi, 254p. Winkler, E. M. 1997 Stone in Architecture; 3rd ed.; Springer-Verlag , Berlin _____________________________________________________________________
    • Importance of Geology in Rock Monuments Dr Vadagbalkar S.K. Page 10 Illustrative Figures: Pitted and rough surface due to vesicles and zeolites (amygdales) in Basalts 1- Ellora caves (Aurangabad) and in 2- Elephanta caves (Mumbai) Marble? Statue! Highly Weathered Weathering in Sandstone 1 2