Big calcite crystal on the left
showing birefringence effect. The spectrum above has a low background.
Calcite has a high intensity Raman scattering as can be seen by the very
small intensity of the filtered laser line at 632.8 nm compared to Raman
intensity. Calcite with its 3 peaks from around 200 cm-1 to
above 1000 cm-1 could also be used to calibrate Raman spectra