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

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PARAGENESIS AND WATER
Profiles also give information related to paragenesis and, indirectly, temperature
(Figure 15). Broad, open absorption features coupled with large water features
such as those found in smectites, zeolites, and opaline silica minerals indicate
ambient to low temperatures from low energy environments. As the profile
sharpens and becomes well defined, such as in muscovites, pyrophyllite,
epidote, and dickite, the temperature of formation increases and the crystal
lattice becomes ordered in a high-energy environment.
Figure 15 - plots showing changes in profile
As a function of ordering in the crystal lattice,
From broad, low temperature smectites to
higher temperature mica and pyrophyllite.
15
Figure 14 - A very important series is the
one from montmorillonite (A) through to
muscovite [I]. This goes through mixed
layer smectite/illite [B] and illite/smectite
[C, D] to illite [E, F, G, H]. The plot
summaries the species in this series and
shows the information that can be gained
by the wavelength shift indicating
changes in aluminum content. This is
the most complicated series commonly
worked with in alteration systems.
Changes in water content, profile shape
and wavelength are all subtle between
the different species in the series. They
are difficult to distinguish and can only
be differentiated by comparison against
references.
Figure 16 - plots different water sites from
channel water in beryl to molecular water
in gypsum to zeolite channel water to
interlayer water in smectite to surface
water.