Single-crystal vibrational spectra of beryl and dioptase

Abstract

Using oriented single crystals of beryl and dioptase, almost the full number of bands predicted by factor-group analysis has been observed in each case. The same [Si₆O₁₈]^12– ring occurs in both minerals; in dioptase, slight distortions caused by the need to provide Cu²⁺ with a tetragonal environment have a profound effect on the spectrum which bears little resemblance to that of beryl. The bonding in both crystals is discussed.