Optical microscope and SEM evaluation of roofing slate fissility and durability

Abstract

The fissility and durability of representative samples of commercial roofing slates from ten deposits in the NW of Spain have been evaluated using transmitted and reflectedlight optical microscopy, scanning electron microscopy, chemical testing and geomechanical procedures. The dominant sulphides in the different slate samples are pyrite and pyrrhotite, the weathering potential of which can be highly variable. The dominant carbonate mineral is ankerite, which explains the low reactivity of these slates in acidic media. The minimum commercial plate thickness varies between 3.5 and 5 mm, depending on the microtexture of the rock. The methodology used in this paper is proposed in order to eliminate the subjectivity of input data that are used in current methods of evaluation and modelling of slate deposits, thus producing an improvement in the profitability of mining operations and a reduction in waste materials.