Fluorite is normally purple to blue, but green, yellow, and brown varieties are possible. The phenomenon contributes to this mineral's electron jumps, in response to ultraviolet radiation, in which the return to the ground state gives off a color glow or fluorescence. Separate from electronic processes are the vibrational processes. These involve the bonds in a lattice or a molecular compound. The frequencies that these molecules absorb depend on the strengths of the bonds and the masses of atoms or ions participating in the movement.
Solids experience smaller vibrations than liquids or gases.
Given a molecule composed of N atoms, there are 3N - 6 normal modes of vibration. Each of these constitutes a fundamental vibration. These overtones normally are weaker. They tend to produce rather diverse and complex spectra. Some spectral troughs come from fundamental vibrations, while others come from overtones.