Our FT-NIR Rocket fibered Fourier-transform spectrometer is a great tool for mineral identification in rock samples. It offers a very broad spectral range of 900 to 2600nm together with a high resolution, both of which are highly desirable features in this application field. For measuring minerals, a reflection accessory is needed. The measurement area should not be too small, in order to average the measurement on a surface which is larger than the typical granularity. Arcoptix offers the Arcsphere-50-Hal, which is an internally illuminated integration sphere (it has a light bulb inside) with a 10mm diameter measurement port. The Arcsphere-50-Hal easily connects to the FT-NIR Rocket using an optical fiber, and a single power supply powers both the spectrometer and the integrating sphere. The internally illuminated integration sphere illumination provides a very bright signal compared to an integrating sphere that is illuminated via an optical fiber, ensuring that you get the best possible signal-to-noise measurement in that shortest possible time.
Figure 1 - FT-NIR Rocket 0.9-2.6 microns with the internally illuminated integrating sphere Arcsphere-50-Hal
Note that the spectrometer and light source will run on 12V DC, so they can powered with a portable or car battery instead of an AC/DC converter. You can bring this spectrometer onto the field!
After taking the usual dark and baseline measurements, the reflection spectrum of the sample rock is easily obtained within a few seconds, simply by placing the rock sample onto the measurement port of the integrating sphere. Note that the integrating sphere measurement port is closed by a sapphire window. This avoids that the inside of the integrating sphere is contaminated, and the window is not scratched easily.
Figure 2 - Measuring a rock sample with the integrating sphere
Below are a few examples of spectra collected in 10 seconds with the above describes system, to give an ides on the signal to noise ratio and resolution.
Figure 3 - Reflectivity of rocks - examples
We performed a library search one the above spectra, using the Labcognition Panorama software and the freely available USGS Digital Spectral Library.
Our samples were successfully recognized as alunite, chlorite and illite and pyrophillite. A screenshot of the search result for the latter spectrum is shown on Figure 4. It can be remarked that the spectrum from the Arcoptix FT-NIR Rocket (above in blue) has an even higher resolution than the spectrum in the database (below in red), making small spectral feature distinguishable.
Figure 4 - Spectrum search using the Panorama software and the USGS spectral library with the Arcoptix FT-NIR spectrometer
