Crystal chemistry and Raman spectroscopy study of bennesherite, Ba₂Fe²⁺Si₂O₇, and rare accessory Ba minerals from Caspar quarry, Bellerberg volcano, Germany

Abstract Barium melilite – bennesherite, Ba 2 Fe 2+ Si O 7 , known only from pyrometamorphic rocks of the Hatrurim Complex in Israel, has been recognised a carbonate–silicate xenolith Bellerberg volcano area Germany. The empirical formula German specimen is as follows: (Ba 1.32 Ca 0.43 Sr 0.23 Na 0.05 K 0.02 ) Σ2.05 (Fe 0.79 Ti 0.06 Mg Al 0.04 Mn 0.03 Zn 0.01 Σ0.98 1.97 . Raman spectrum bennesherite exhibits presence main vibrations related to 4 tetrahedra and disilicate groups at T1 T2 sites, 589 cm –1 range 618–673 respectively. Detailed spectroscopic analyses performed for two different random orientations confirm reduction bands intensity number some components several spectral ranges. Moreover, heavy atom indicates decrease band frequencies compared melilites with X position. A single-crystal X-ray diffraction experiment, despite attempts, could not be carried out due poor quality small size crystals however, combination composition data allowed accurate phase identification. mineralogical investigations distinguished rare minerals association such walstromite, fresnoite celsian, along various ferrous melilites. Some detected phases are described xenoliths first time. uniqueness mineralisation reflected interaction alkaline magma compositions, which suggests that this locality still deserves attention source new unique minerals.