Pressure shifts of optical absorption bands in iron-bearing garnet, spinel, olivine, pyroxene, and periclase

The shift of crystal field bands due to Fe2+ and Fe3+ has been measured as a function of pressure up to 50 kbar at room temperature. We have examined spin-allowed transitions in the infrared and spin-forbidden transitions in the visible and ultraviolet in spinel, periclase, pyroxene, olivine, and garnet. The pressure shifts of the ferrous bands in the infrared are a measure of the crystal field splitting Δ; the pressure coefficient of energy E = ∣Δ∣ in different materials qualitatively obeys the relation dE/dP = (m/n)E/K, where P is pressure and K is the bulk modulus. However, there appears to be sufficient local relaxation about the iron sites that m/n is closer to 1.3 than to the theoretically predicted 1.67.