Amphibolite: amphiboles, biotite, quartz, dolomite, chlorite and
Locations of areas 1 to 3 in plane
polarized view and cross polars image.
Areas 1 and 7 (images below) are amphiboles
of the hornblende family with a pleochroism from green to yellow. The
best match for the Raman spectra on the left is the sodium-calcium
The brown pleochroic mineral (light brown to deep
brown) is Biotite as shown in the spectrum on the left. Some of the
biotite are cut perpendicularly to the acute bisectrix and thus appear
very dark in the crossed polars view because the angle 2V between optic
axes is very low.
The mineral of low birefringence in
area 3 is evidently quartz as can be easily recognized in LPA view.
Note that the
brown biotite crystal at the top of the image is dark in the LPA view.
The high birefringence material in
area 4 is dolomite.
The green crystal with very low birefringence in
spot 5 (they appear very dark in LPA) is a material belonging to
the chlorite family.
Area 7: another example of the amphibole crystals.
Raman spectrum 7 is reproduced in the first figure at the
top of this page.
Opaques minerals in this section: magnetite.
Reflection image in plane polarized
light: magnetite has a higher reflection coefficient than the silicates
Below is the
reflection image between crossed polars.
The blue curve on the left is the Raman
spectrum obtained with an helium neon laser whose power has been reduced
with a filter. The mineral is magnetite. Two small sharp peaks of an
oxidation product are visible in the spectrum. If the full laser power
is used, high additional peaks of oxidation can be seen.