Spectrum of an Anatase single crystal. (Blue and red curve with the
Raman microscope described here). Notice the high influence of crystal
orientation on the spectrum. Peaks at 400 and 520 cm-1 almost disappear
when crystal is rotated. The peak at 150 cm-1 is still visible with our
microscope even if it appears in the filter transition region due to its
Polished section of a chromite. Our spectrum is closer to the
magnesio-chromite from the RRUFF database taken with a laser at 785 nm.
A polished slab has been cut in the rock shown here. Our Raman spectrum
seems to be the sum of two minerals contributions : Hematite and
Goethite. The double peak at 400 cm-1 and the peak at 550 cm-1 are found
in the Goethite spectrum. Maybe reaction with moisture at the surface of
the section. A new spectrum after repolishing can be seen below.
The rock shown on the left side was sold as ilmenite. The
Raman spectrum is not similar to Ilmenite. With the help of the
RRUFF database a first interpretation was the following: the
section on the left seems to be close to a mineral called Armalcolite, a
magnesian Ilmenite. A careful polishing of the sample allowed a
reflection coefficient to be measured: it is close to the Hematite
reflecting power. A second spectrum with the new spectrograph is
reported in the figure below. It seems now that the new spectrum could
be interpreted as hematite in agreement with the reflection coefficient.
In the same figure, a new spectrum of the hematite above has also
been recorded with the new spectrograph just after repolishing the
One of the octahedron magnetite crystal found on the rock reproduced on the left
side has been used to record the Raman spectrum. Magnetite has a 3 peaks
spectrum quite similar to the reference.
A polished slab has been cut from the sample shown. The spectrum I have
found on this sample is characteristic of pyrite rather than marcasite
as can also be seen on the pyrite sample below. I should investigate
further with other samples to find a real Maracasite Raman
Spectrum of a polished Pyrite sample is shown above, quite similar to
the reference spectrum from the RRUFF database.
Elemental Silicon is often used in the literature to calibrate the
wavelengths of Raman spectrographs. I have polished a few silicon flakes
as shown on the left to record this Raman spectrum nearly composed of
one single peak.
The bright mineral Skutterudite on the left gave the Raman spectrum
above. My spectrum is similar to the references but not identical. The
high noise level of these spectra is due to the low Raman scattering Skutterudite.