An overview of vis-nir-swir field spectroscopy - Spectral International

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concentration, water content and environmental considerations. For mineral
identification, that signature is compared against characterized references for a
validated identification. This can be done manually by using wavelength tables
and overlaying references on the unknown or it can be done using computer
algorithms operating against a database of references (i.e., a spectral library).
For best results these libraries must be set up for specific deposit types, and not
allow the algorithm to make a wrong choice.
Figure 2 – Example absorption spectrum. The units for the horizontal scale are in
nanometers or microns while the vertical scale is percent reflectance. The absorption
figure shown is a doublet, with two minima or lowest points of the feature. Each
minimum has a distinctive wavelength, which is a function of the chemical
composition. “FWHM” means Full Width at Half Maximum. It can be used for
symmetry determinations that are related to crystallinity.
Although the computer algorithms are useful for data management and
organization, care must be taken when using them for phase identification and
quantification. There are many unaddressed variables and non-user chosen
identifications are not always accurate. Additionally, important information on
crystallinity, water, organics, and iron, among other things, is lost.
VISIBLE RANGE SIGNATURES
There is an abundance of information to be gained from the visible region of the
EMS. This is one of the features that makes the full-range spectrometers so
valuable. Figure 3 shows some of the cations that are recognizable by colors
and corresponding minerals. Although the visible range is constrained from 300-
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