NIR and petrology

“Petrology is the study of rocks – describing their characteristics such as composition, texture, structure, occurrence and distribution; and determining the conditions and processes that formed them.” [5]

The value of full-range spectrometers for petrology:

• “Spectra, like human fingerprints, can be used to search for materials with a similar spectrum and to investigate the composition of the material.” [7]
• “Diffusive spectral reflectance (DSR) has been successfully used as a geologic tool to identify mineral phases in rocks and sediments. The method is non-destructive, fast, and relatively inexpensive.” [4]
• “Scattering properties are wavelength-dependent and can vary significantly over the VIS–NIR spectral range. In particular, the phase function of a granular material is affected by both the absorptivity and the external and internal structure of the grains, from the millimeter scale down to the wavelength scale.”[6]
• ”Reflectance spectroscopy can yield valuable information on metamorphic intensity in rocks containing white mica, particularly in low-grade sequences where conventional indicators of metamorphic grade are lacking. Furthermore, this information can be obtained with field-portable spectrometers.”[1]
• “The main benefit of using the field spectrometer was the ability to provide information relevant to understanding the variations in mineralogy and, by inference, rock types at a given location. This information was mandatory in deciding the overall exploration strategy. By incorporating estimates of rock types and their distributions, the geology/geomorphology team improved their understanding of the regional geology and history of the landforms present in the field area.”[3]

The solution

The ASD TerraSpec spectrometers are portable with optimal signal-to-noise design for faster measurements, and wide spectral coverage of 350-2500 nm for determining a variety of important geological parameters.

We offer different instrument configurations and many accessory options for a variety of set-up and sampling approaches for the most convenient and productive measurement scenarios.

ASD instruments offer a practical solution for applications in Petrology.

The TerraSpec 4 Mineral Analyzer can be used in the field or the lab; accurately measures a wide variety of geologic samples, including clays and other alteration minerals. The high signal-to-noise ratio of this spectrometer allows for accurate measurement of even dark rocks containing an abundance of iron silicate minerals.

The TerraSpec Halo Mineral Identifier is an all-in-one full-range spectrometer (350-2500 nm) including the visible and short-wave infrared regions. Halo includes an onboard GPS producing GIS compatible information, audio recorder and internal wavelength standard to allow for easy operation, and efficient instrument status monitoring. It also features ASD’s proprietary, state-of-the-art mineral identification software for one click mineral-identification of up to seven minerals contained in a natural sample in the field or the lab.

• Extensive spectral library with multiple examples of minerals, fully validated to ensure identification accuracy.
• Multi-mineral predictions, confidence levels and spectral scalars that allow the monitoring of crystallinity changes, subtle shifts in composition and alteration patterns associated within geochemical and geothermal gradients.

Figure 1. Real-time mineral identification with the TerraSpec Halo in Death Valley, California (US). [2]

Halo Manager, the desktop computer-based software, allows for the configuration of the TerraSpec Halo instrument, display of Halo spectra and mineral identification results, and exporting of the data to third-party software programs like The Spectral Geologist (TSG®) Pro mineral analysis software by AusSpec

• Export GPS coordinates and mineral identification to ENVI® and GIS.

Ideal for Petrology applications:

• Field-portable solution
• Non-destructive
• Grain-size independent
• Little to no sample preparation
• Simple, rapid and cost effective real-time measurement (data analysis in the field) 
• Digital instrumental record, processes can be automated
• Tie mineralogy at the outcrop scale to that seen in remotely sensed multispectral and hyperspectral images

References

^{1. Duke, E.F., and Lewis, R.S. (2010). Near infrared spectra of white mica in the Belt Supergroup and implications for metamorphism. American Mineralogist, 95, 908-920. doi: 10.2138/am.2010.3281}

^{2. Duke, E.F. (2016). NIR, Metamorphic Petrology & Remote Sensing [Video Webinar]. Retrieved from http://www.asdi.com/learn/resources/videos/nir-metamorphicpetrology- and-remote-sensing.}

^{3. Gazis, P., Newsom, H.E., & Stoker, C. (2001). Geological characterization of remote field sites using visible and infrared spectroscopy. Journal of geophysical research, 106(E4), 7683-7711.}

^{4. Hubbard, M. (2003, November). Application of VIS/NIR spectral reflectance in sourcing and recognition of heat-treatment in cherts. In 2003 Seattle Annual Meeting.}

^{5. Memorial University of Newfoundland (MUN). (2014, September 2). Petrology and Mineralogy. Retrieved from http://www.mun.ca/earthsciences/Research/Areas_of_Research/Petrology.php.}

^{6. Pilorget, C., Fernando, J., Ehlmann, B. L., Schmidt, F., & Hiroi, T. (2016). Wavelength dependence of scattering properties in the VIS–NIR and links with grain-scale physical and compositional properties. Icarus, 267, 296-314.}

^{7. Qiu, J.T., Li, P.J., Yu, Z.F., & Li, P. (2015). Petrology and Spectroscopy Studies on Danxia Geoheritage in Southeast Sichuan Area, China: Implications for Danxia Surveying and Monitoring. Geoheritage, 7(4), 307-318.}