When excited by the laser, some minerals will fluoresce.
Fluorescence is a common problem for Raman. Fluorescence is a much stronger response than Raman scattering and will flood the detector, obliterating the weaker Raman signal.
Rare earth elements for example are common culprits for causing fluorescence.
The Bruker BRAVO Raman uses Sequentially Shifted Excitation (SSE) algorithms for fluorescence mitigation. This aims to remove fluorescence from the spectra to resolve the Raman signal.