To study the features of the local structure of minerals in the lamprophyllite group, vibrational spectroscopy methods (IR and Raman) are used to investigate fluorine-dominant holotype representatives of this group (fluorbarytolamprophyllite, lileyite, and emmerichite), as well as the related mineral schüllerite. It is shown that an increase in iron content at the L-site (L = Ti, Fe3+) with a coordination number of 5 is accompanied by elongation of the L–O bond and a decrease in the proportion of Ti=O titanyl bond and, as a consequence, a decrease in the frequency of symmetric stretching vibrations of Ti = O–M1. In the case of lileyite, the decrease in the frequency of these vibrations may also be associated with partial substitution of Na at the M1-site by Ca. It is established that the most intense band of apical Si–O stretching vibrations in the Raman spectrum of lileyite is split into components at 867 and 898 cm–1, unlike the spectra of other minerals. The most probable cause of this splitting is the mixed occupancy of the adjacent M2-site, where 55% of the occupants are divalent cations (predominantly Ca2+ with admixtures of Fe2+ and Mn2+).
Aksenov et al. (Sun,) studied this question.