Cuantificación mediante estudio estereológico del sistema microfisural del granito de El Berrocal (Sistema Central, Toledo, España)



This paper describes an exarnple of the use of stereological techniques for the quantification of some characteristics of the microcrack network of rocks, in this case the El Berrocal granite (Sistema Central, Toledo, Spain). From data measured in sections, therefore 2-D, 3-D characteristics of the microcrack network have been obtained. The quantified characteristics are the microcrack density (in terms of the frequency distribution of the specific surface of microcracks in relation to their apertures) and the relative frequency of the microcrack aperture. These procedures have been applied to images under scanning electron microscopy, so microcracks with apparent apertures over 0,l pm. have been measured. The so called "vertical sections" have been prepared to assure a correct sampling. From the measurement of the apparent apertures of microcracks and applying stereological procedures, the real apertures and the specific surface of each class of microcracks are obtained. Besides of the characteristics of the microcrack network of the rock as a whole, data of the microcracks associated to each of the main minerals (quartz, feldspars and micas) are presented separately, allowing the interpretation of the contribution of each mineral to the microfractography of the rock. In El Berrocal granite, the microcracks with a real aperture less than 1 m are the most abundant. The microcracks are more important in quartz and, above all, in feldspars (with more than 60% of the total network of the rock), than in micas. When considering the microcrack density of each mineral, and taking into account the mineral composition of the rock too, the feldspar is also the more cracked mineral in the rock. Nevertheless, the frequency distribution of the specific surface in relation to the microcrack aperture is quite similar in any of the three mirierals. It is intended with this paper to show the possibilities of the stereology that, using simple, fast and economic procedures, provides quantitative information about the characteristics of the microcrack network of rocks that can be very useful in many geological studies.

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