Rapid quantitative mineral and phase analysis using automated scanning electron microscopy (QemSCAN); potential applications in forensic geoscience

Abstract

QemSCAN is a scanning electron microscope (SEM) system, initially designed to support the mining industry by providing rapid automated quantitative mineral analyses. The system is based upon Carl Zeiss SEMs fitted with up to four light-element energy dispersive X-ray spectrometers. Representative subsamples are mounted into either resin or wax blocks and polished prior to analysis, or can be mounted onto carbon tape. During analysis, X-ray spectra are collected at a user-defined pixel spacing and are acquired very rapidly (c. 10 ms per pixel). The measured spectra are automatically compared against a database of known spectra and a mineral or phase name is assigned to each measurement point by the QemSCAN computer software programs. In this way the near-surface qualitative elemental composition of each particle is systematically mapped, assigned to a mineral name or chemical compound/species, and digital pixel maps of each particle are created. Depending upon a range of parameters, including the particle size and the user-defined pixel spacing (which can vary between 0.20 μm and 25 μm), approximately 1000 particles, each 1–10 μm in size, can be measured per hour using a 1 μm pixel spacing. In addition to providing a qualitative elemental analysis and mineralogical or phase assignment for each particle, data relating to particle size, shape and calculated specific density are also generated. In this study, the potential application of this automated SEM system in forensic geoscience was evaluated by the analysis of: (1) a series of soil samples, and (2) a series of dust samples from an industrial complex. In both case studies, the mine-ralogy/phase composition of each sample analysed was found to be distinctive. In addition, textural data for the soil samples and particle shape data for the dust samples show that they can be clearly distinguished. Automated SEM using QemSCAN has clear potential application in the analysis of soil or other trace evidence in forensic case work.

A critique of the present use of some geochemical techniques in geoforensic analysis

“…Perhaps in such circumstances it would be better not to use elemental chemical analyses at all (given the inherent problems that such techniques pose, as outlined above). If geochemical analyses were required, perhaps XRF analysis (which has been recognised as having greater accuracy [9]) or XRD analysis, that is able to provide mineralogical data from small samples [11], or indeed QemSCAN analysis [12] would be more appropriate.…”

Microstructural characterization of alkali metal mediated high temperature reactions in mullite based refractories

“…The system is based upon a Zeiss E340 scanning electron microscope with four energy dispersive x-ray spectrometers (EDS). The resulting x-ray and backscattered electron signals (BSE) are compared with a database of known minerals and amorphous phases to produce a mineralogical identification [10][11][12]. Species with similar EDS-spectrum such as magnetite and hematite, can be differentiated by different BSE signal, while it is still difficult to separate magnetite and wüstite, since the software does not differentiate crystal structures [13].…”

Trace element mobility in a polluted marine sediment after stabilisation with hydraulic binders

“…Each spectrum is allocated to a specific mineralogy and sample mineralogy is inferred from the chemical spectra acquired and false colour images allow the visual comparison of samples (van Veen et al, 2013a(van Veen et al, , 2013b. A review of the QEMSCAN® applications is given by Pirrie et al (2009) and further details can be found in Gottlieb et al (2000); Pirrie et al (2004) and Pirrie and Rollinson (2011).…”