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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Referência Bibliográfica

ZANON, V., PECCERILLO, A., CONVERSINI, P., PACHECO, J., PIMENTEL, A. (2007) - Utilization of photographic techniques to Recognize Zeolitized facies in the orvieto ignimbrite, as potential pollutant for the underneath Acquifer. IUGG XXIV General Assembly, Perugia, Itália, 02 - 13 Julho (Poster).​


The weathering condition of a volcanic rock is of remarkable importance to the definition of its geotechnical characteristics, and in view of its possible future application to civil engineering. Zeolitization, caolinization oxidation, fumarolization, change partially, or even totally, the initial composition of a rock, modifying its original geochemical structure through the selective removal of some elements, the deposition of new minerals and the modification of its molecular structure.


The most common of these processes is zeolitization of volcanic glasses, which leads to the total loss of the original textural characters of a rock. Such a process has great influence on the geotechnical characteristics of a deposit, causing it to become highly resistant to compression, so that the originally loose pyroclastic rocks acquire pseudolithoid behaviour. But the presence of zeolites inside a rock can also cause some problems of environmental pollution, due to their capability of bearing fluids in their crystalline structure. Therefore, the possibility of discriminating facies on the basis of their different zeolitic content, in the study of a remarkably extensive formation, is of great importance to present time investigations.


In consideration of the typical reddish colour of zeolitized pyroclastic formations, the possibility and feasibility of applying photographic techniques to give evidence to the presence, extent and distribution of zeolitic facies was evaluated and applied.


This methodology consists in sampling colour tones (in accordance to RGB values scale), and then measuring their intensity in each rock specimen through the utilization of Maxwell diagram. All the digital images were obtained under standardized capture conditions (digital filter sensitivity, lens angle, diaphragm, light intensity and temperature, light angle of incidence, focusing distance, etc.) and, afterwards, they were checked using equivalent values of colour intensity.


This methodology, applied to samples from a pyroclastic flow of the Vulsini Volcanic District (Central Italy) showed a good correlation between the RED percentage values and the extent of zeolitization occurring in the different deposits, and thus allowed a fast discrimination of potentially hazardous facies within the deposit.