Andalusite Visible Spectra (380 - 1100 nm)
Andalusite's greenish yellow color comes from Fe3+.
If Mn3+
is in the structure, a dark green color results. The intense
brownish-red
color observed for light polarized in the c direction is the result of
strong absorption from the Fe2+
- Ti4+
intervalence
charge transfer centered near 480 nm. Many samples contain an admixture
of colors from Fe, Ti and Mn. Varieties containing vanadium [V3+]
and chromium are known which have reddish-brown colors.
Image of the andalusite absorption spectrum
- GRR
278 spectrum;
from
Santa Teresa district, Espírito Santo, Brazil. 0.912 mm thick sample. The color of this
material
varies considerably with the direction in which it is observed. It
varies
from yellowish green to a hard-to-describe blend of red and green. Data
Files: E||a; E||c;
- GRR
375 spectrum;
a lavender
crystal from Tenderfoot Mountain, near Custer, South Dakota, USA. 0.951
mm thick sample. Data files: E||a;
E||c;
- GRR
Llano spectrum;
The
core region of a reddish brown crystal from the Llano uplift, Texas,
USA
which contain about 0.81 wt% vanadium (expressed as V2O3)
and about 0.09 wt% chromium. Presented for a 0.110 mm thick sample.
Data
files: alpha
= E||c; beta
= E||b; gamma = E||a.
- MT-Brazil;
Color zoned crystal
from Brazil. 0.79 mm thick crystal with all data normalized to 1.0 cm.
The crystal contains 0.35 wt% FeO and a trace amount of titanium. Note
the difference in the intensity of the Fe-Ti intervalance charge
transfer band near 480 nm between the spectrum of
the light zone and spectrum of the
dark zone. Data Files: Contributed data from
Michail Taran, Kyiv, Ukraine: light zone: E\\a, E\\b, E\\c.
Dark zone: E\\a,
E\\b,
E\\c.
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to the
list of visible data files
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to the Index to Data Files
