Pyroxenite (1)

                                                                   Thin section of a pyroxenite coming from Malaga (Spain).

 

The section is mainly made up of big orthopyroxene crystals. The region shown here exhibits higher birefrengence crystals, colorless in non analyzed light.

This picture has been photographed with a Benford plate (double quarter wave plates perpendicular to each other). The black area at the center of the image is a hole in the section.

Below is the spectrum recorded on one of the big low birefringence crystal. This spectrum is characteristic of orthopyroxenes with a strong absorption at 900 nm due to Fe2+. This absorption is sufficiently strong to be seen in a 30 thickness section.

 

The same pyroxenite material in a thick section (200) viewed in plane polarized light. Both images have been photographed by rotating the polarizer by an angle of 90. The pleochroism of the orthopyroxenes from yellow-green to pink-brown can be seen. The transparent colorless crystals at the top of the image correspond to the high birefringence material seen in the thin section above.

The NIR spectra of both regions are illustrated below. Curves red and blue have been recorded on a colorless crystal. The spectra show the three peaks already observed on olivine material. The other spectra in the figure were recorded on two different orthopyroxene crystals. The intesity of the big 900 nm absorption depends of course on the crystal section and orientation in the polarized light. Notice the onset of the second absorption peak at 1600 nm.

 

 
   

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