A method for the determination of the levels of asbestos fibres in ophiolitic rocks used in construction and industrial applications

In this paper, we propose a method for the quantification of asbestiform minerals in ophiolitic rocks. This method was tested on actinolite and chrysotile occurring in mafic and ultramafic rocks from several ophiolites from Greece and incorporates a combination of techniques of identification and measurement of asbestiform minerals, including polarising microscopy, X-ray diffractometry (XRD), scanning electron microscopy (SEM) and image analysis of specifically acquired images. Polarising microscopy precedes the procedure, as it is the first tool for a geologist to identify rocks and minerals including toxic ones. XRD indicates the existence of one or more of the above-mentioned potential asbestiform minerals; however, it has the disadvantage of the lack of any information about the shape and dimensions of the crystals. Hence, we employed detailed SEM observation and measurements, in order to specify which grains display asbestiform habit. Computational methods enabled rapid size measurements and quantification of asbestos fibres. The presence of non-asbestiform actinolite crystals must be considered with care because we observed that some particles are partially separated along cleavage from coarse grains. Hence, although non-asbestiform crystals may be initially present in a raw material, it is not unlikely that asbestos fibres may be generated during the production processes and inservice deterioration of aggregates.