Asbestos determination in ophiolitic rocks by Image Analysis coupled with Raman Spectroscopy

The determination of the asbestos content in ophiolitic rocks is carried out by well-known and standardized analytical techniques (SEM-EDS according to Italian regulation on environmental parameters on spoils, waste and rock and soil). Despite the high resolution and the possibility to obtain elemental information, SEM-EDS is not always able to discriminate serpentine minerals, including chrysotile and non-regulated fibrous antigorite, lizardite, and possibly polygonal serpentine.

Moreover, the analytical procedures using electron microscopies are time-consuming and show an intrinsic lack of statistical representativeness, due to the low portion of the analytical sample that is effectively analyzed. Conversely, optical microscopy delivers fast results affected by a lower resolution and unreliable mineral fibre identification. Many sectors related to the realization of geo-engineering projects would take enormous advantages from a more efficient and statistically-sound approach.

To evaluate the results obtained from a state-of-the-art optical microscope with automatic image analysis in-line with micro-Raman spectrometer, we designed a study to comparatively determine the asbestos content from a large set of samples deriving from asbestos-bearing rock of the ophiolitic domain. The performance of a Malvern G3 Morphology microscope equipped with a 850 nm laser Raman spectrometer was tested on 40 samples. The same samples, prepared from ophiolitic rocks from the Ligurian Alps comminuted down to top-size = 100 μm, were parallelly analyzed and results compared with SEM-EDS quantitative method described by Italian regulation (Ministerial Decree 6 September 1994, All 1B).