Raman spectroscopy is a form of vibrational spectroscopy where the compound or mineral is identified.
A monochromatic light from a laser is directed onto a sample. Most of this light scatters and remains the same frequency (Rayleigh), however a small percentage is absorbed and re-emitted as a process of vibrating (bending and stretching) the chemical bonds (Raman).
Diagram of Rayleigh and Raman scatter on a eucryptite sample.
This process changes the frequency (energy) of the re-emitted light and this subtle shift in frequency is measured by the Raman (Raman shift). The vibrational modes and their associated energies are unique to each compound or mineral, generating a unique spectrum which may be identified through spectral matching.