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Quantitative Modal Determination of Geological Samples Based on X-ray Multielemental Map Acquisition

Published online by Cambridge University Press:  14 June 2002

Roberto Cossio ,
Alessandro Borghi  and
Raffaella Ruffini
Roberto Cossio
Affiliation:
Dipartimento Scienze della Terra, University of Torino, Via Valperga Caluso 35, 10125 Torino, Italy
Alessandro Borghi
Affiliation:
Dipartimento Scienze Mineralogiche e Petrologiche, University of Torino, Via Valperga Caluso 35, 10125 Torino, Italy
Raffaella Ruffini
Affiliation:
Dipartimento Scienze Mineralogiche e Petrologiche, University of Torino, Via Valperga Caluso 35, 10125 Torino, Italy
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Abstract

Multielemental X-ray maps collected by a remote scanning system of the electron beam are processed by a dedicated software program performing accurate modal determination of geological samples. The classification of different mineral phases is based on elemental concentrations. The software program Petromod loads the maps into a database and computes a matrix consisting of numerical values proportional to the elemental concentrations. After an initial calibration, the program can perform the chemical composition calculated on the basis of a fixed number of oxygens for a selected area. In this way, it is possible to identify all the mineral phases occurring in the sample. Up to three elements can be selected to calculate the modal percentage of the identified mineral. An automated routine scans the whole set of maps and assigns each pixel that satisfies the imposed requirements to the selected phase. Repeating this procedure for every mineral phase occurring in the mapped area, a modal distribution of the rock-forming minerals can be performed. The final output consists of a digitized image, which can be further analyzed by common image analysis software, and a table containing the calculated modal percentages. The method is here applied to a volcanic and a metamorphic rock sample.

Keywords

modal analysismicroanalysispetrologyX-ray mapsgeological samplesmineral chemistry
Type
MATERIALS APPLICATIONS
Information
Microscopy and Microanalysis , Volume 8 , Issue 2 , April 2002 , pp. 139 - 149
Copyright
2002 Microscopy Society of America

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