Garnet spectrum (Pyrope).

 

 

Thick section of a garnet. The spectrum is shown below.

This piece of crystal has been bought as a tourmaline section perpendicular to the optic axis thus non pleochroic. In fact, after Raman examination, the mineral was identified as a garnet (pyrope type).

The high intensity bands in the NIR region are absorptions due  to Fe2+ crystal fields transitions. A third band is also normally present at higher wavelengths beyond the range of the present spectrometer.

Small forbidden transitions typical of Pyrope - Almandin series can also be seen in the visible below 700 nm.

 

The pink crystal shown above is a pyrope garnet as can be seen on the Raman spectrum below.