THE EFFECT OF SALTS ON THERMAL AND HYDRIC DILATATION OF POROUS BUILDING STONE*

Fifteen desalinated sandstone drill core samples from Umm Ishrin Sandstone Formation in Petra (Cambrian age) were used for this study. The samples were mineralogically analysed using X‐ray diffraction and their physical properties were also determined. Samples with similar physical properties and mineralogical composition were taken for further experimental work. After desalination, thermal and hydric dilatation coefficients were measured, then three types of salts (NaCl, KCl and Na₂SO₄·10H₂O), which have high solubility and consequently are the most dangerous to building stone (and are also detected in the sandstone monuments in Petra), were introduced into the samples and their contents were calculated. The results show that salt crystallization in the pores of building stones can increase their thermal dilatation and decrease their hydric dilatation to varying extents, depending on the nature of the salt. The average increase in the thermal dilatation coefficient per unit mass of salt is the lowest for the Na₂SO₄·10H₂O‐salted samples with a value of 5.3%, while the NaCl‐salted samples have the highest value with 7.8% per salt mass. The average percentage of the decrease of the hydric dilatation coefficient is 1061% for Na₂SO₄·10H₂O‐salted samples per mass of salt content; the NaCl‐salted samples have a value of 1510% per mass of salt content, and the KCl‐salted samples almost the same value. For the salt‐free samples, it was found that in climatic conditions with a high temperature range, the deterioration of sandstone due to temperature fluctuation is more effective than that caused by change in the moisture content, while samples with high salt content suffer more from hydric dilatation.     

APPLICATIONS OF PETROGRAPHY AND ELECTRON MICROPROBE ANALYSIS TO THE STUDY OF INDIAN STONE SCULPTURE*

Examples of research on ancient Indian stone artefacts utilizing petrographic examination coupled with qualitative and quantitative electron beam microprobe analysis of specific minerals are described. Types of artefacts discussed include Gandharan schist sculptures. Pala dynasty phyllite and schist objects from eastern India, Hoysala sculptures from Karnataka state (southern India), and sandstone objects from northern India. In spite of the rich history of stone sculpture in the Indian subcontinent, characterization studies to date have been limited in scope, typically involving unprovenanced artefacts. The examples described point to areas in which more extensive research could produce useful information for the provenancing of artefacts.     

The Construction Process of the Angkor Monuments Elucidated by the Magnetic Susceptibility of Sandstone*

The Angkor monuments in Cambodia are mainly constructed of grey to yellowish‐brown sandstones. No differences in the constituent minerals and in the chemical composition of the sandstones have been confirmed among the monuments. However, we have found their magnetic susceptibility a useful parameter by which to distinguish them. The principal monuments of Angkor Wat, Ta Prohm, Preah Khan, Banteay Kdei and Bayon, constructed from the Angkor Wat period to the Bayon period (from the beginning of the 12th century to the beginning of the 13th century ad ), were investigated in detail using a portable magnetic susceptibility meter. We succeeded in dividing the periods of construction into stages. This elucidated the enlargement process of the monuments and correlated their construction stages.     

PROVENANCE OF THE SANDSTONE USED IN THE CONSTRUCTION OF THE KHMER MONUMENTS IN THAILAND

We investigated the sandstone used in the construction of the Khmer monuments situated upon and around the Khorat Plateau in north‐east Thailand in order to clarify the provenance. The sandstones of the 22 investigated Khmer monuments can be classified into three groups. The sandstone of Group 1 is lithic and is derived mainly from the Khok Kruat Formation. This group includes the sandstone used at Phimai, Phnom Wan, Muang Khaek etc. The sandstone of Group 2 is siliceous and can be subdivided into three further groups. The sandstone of Group 2 is considered to have been derived from the Phu Phan, Phra Wihan or Sao Khua Formations. The sandstone used at Muang Tam, Phnom Rung, Sdok Kok Thom, Preah Vihear (Khao Phra Wihan), Narai Jaeng Waeng etc. belongs to Group 2. The sandstone of Group 3 is feldspathic and is correlated with the grey to yellowish‐brown sandstone that is commonly used in the Angkor monuments in Cambodia. This sandstone is used at Wat Phu and Hong Nang Sida in Laos. The above results reveal that the choice of sandstone used for the Khmer monuments, including the Angkor monuments, was dictated by the surrounding geology.     

TOWARDS A QUANTITATIVE PETROGRAPHIC DATABASE OF KHMER STONE MATERIALS—KOH KER STYLE SCULPTURE

A comprehensive quantitative petrographic database of sandstones used by the Khmers for sculptural purposes would be a helpful tool for archaeologists, museum curators and others interested in pursuing research on early stone usage, geological source and provenance. Towards that end, this paper presents quantitative petrographic analysis of stone materials used in the production of some free‐standing sculptures and architectural elements in the Koh Ker style of the 10th century from the collections of the National Museum of Cambodia and The Metropolitan Museum of Art. These materials are compared to samples from the quarry of Thmâ Anlong near the foothills of the Phnom Kulen, Sieam Reap province. Primary and secondary detrital modes and key grain‐size parameters are used to identify three sandstone types. The free‐standing sculptures are carved from feldspathic arenite and feldspato‐lithic to litho‐feldspathic arenite. Finely carved lintels are worked from a quartz arenite, which is significantly richer in quartz grains and of a finer grain size. The geological source of the two other lithotypes will have to await detailed geological survey of the Koh Ker area accompanied by petrographic study of selected samples from documented quarries. The significance and potentiality of quantitative petrographic study of Khmer stone materials are shown in supporting and integrating archaeological investigations in South‐East Asia.