Elucidating Rock and Mineral Composition With Handheld Agilent FTIR Analyzers

Significance of the Topic

Field-deployable FTIR analysis addresses the need for rapid, in-situ identification of mineral composition and molecular structure in rocks, soils and sediments. By capturing information on covalent bonding such as carbonate, sulfate and silicate groups, handheld FTIR complements elemental data from XRF, enabling a comprehensive understanding of geological samples on site without extensive preparation.

Objectives and Overview

This application note presents the capabilities of Agilent handheld Fourier transform infrared analyzers optimized for diffuse reflectance measurements of geological specimens. The goal is to demonstrate how mid-IR spectra reveal molecular bonding in minerals, verify sample identity against a library, detect contaminants or secondary phases, and support field decision-making alongside portable XRF devices.

Methodology and Instrumentation

• Handheld analyzers: Agilent 4100 ExoScan and 4300 FTIR with integrated diffuse reflectance interface for direct field measurement
• Diffuse reflectance sampling: direct contact, optional abrasion with silicon carbide paper and dilution using KBr to reduce restrahlen bands
• Spectral library development: onboard storage of over 1000 mineral spectra enabling rapid library search
• Complementary use of XRF: elemental screening informs FTIR interpretation of molecular structure

Main Results and Discussion

• Identification of major mineral classes: distinct IR fingerprints for carbonates, sulfates, phosphates, silicates and others allow unambiguous matching against library spectra
• Quality control of reference collections: analysis of white mineral specimens labeled as gypsum, celestite, barite and calcite revealed predominance of calcite in all four via carbonate bands, correcting mislabeling
• Detection of secondary components: examination of lignite coal samples revealed water content variations and unexpected kaolin clay through sharp OH stretching bands at 3700–3600 cm-1, highlighting trace contaminant identification
• Reflectance artifacts and preparation: restrahlen bands appear as negative peaks in undiluted samples, while sanding and KBr dilution yield true positive absorbance spectra with consistent peak positions

Benefits and Practical Applications

• Rapid onsite mineral chemistry assessment, including hydration states, polymorphs, crystallinity and organic content
• Real-time decisions on sample relevance and mapping of site variability without sending materials to laboratory
• Enhanced light element sensitivity (H to Si) and molecular bonding information not accessible by most XRF systems
• Improved QA/QC in mining, environmental geochemistry, construction materials and hydrocarbon exploration

Future Trends and Possibilities of Use

The integration of handheld FTIR data with GIS and remote sensing platforms will enable dynamic mapping of mineral distributions. Expansion of onboard spectral libraries using machine learning algorithms can automate identification of complex mixtures. Emerging applications include continuous monitoring of soil remediation, in-line process control in mining operations and environmental assessment of trace contaminants.

Conclusion

Agilent field-ready FTIR analyzers provide geoscientists with vital molecular bonding information that complements elemental analysis by XRF. The ability to perform diffuse reflectance measurements directly on geological specimens accelerates accurate mineral identification, detects impurities and supports informed decision-making in the field, reducing reliance on laboratory workflows.