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Crystal chemistry of lamprophyllite‐group minerals from the Murun alkaline complex (Russia) and pegmatites of Rocky Boy and Gordon Butte (USA): single crystal X‐ray diffraction and Raman spectroscopy study
Author(s) -
Aksenov Sergey M.,
Ryanskaya Anastasia D.,
Shchapova Yuliya V.,
Chukanov Nikita V.,
Vladykin Nikolay V.,
Votyakov Sergey L.,
Rastsvetaeva Ramiza K.
Publication year - 2021
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520621000354
Subject(s) - butte , pegmatite , raman spectroscopy , crystal chemistry , chemistry , crystallography , crystal structure , alkaline earth metal , group (periodic table) , crystal (programming language) , x ray crystallography , mineralogy , diffraction , geology , alkali metal , physics , organic chemistry , optics , paleontology , programming language , computer science
Specific features of the crystal chemistry of lamprophyllite‐group minerals (LGMs) are discussed using the available literature data and the results of the single‐crystal X‐ray diffraction and a Raman spectroscopic studies of several samples taken from the Murun alkaline complex (Russia), and Rocky Boy and Gordon Butte pegmatites (USA) presented here. The studied samples are unique in their chemical features and the distribution of cations over structural sites. In particular, the sample from the Gordon Butte pegmatite is a member of the barytolamprophyllite–emmerichite solid solution series, whereas the samples from the Murun alkaline complex and from the Rocky Boy pegmatite are intermediate members of the solid solution series formed by lamprophyllite and a hypothetical Sr analogue of emmerichite. The predominance of O 2− over OH − and F − at the X site is a specific feature of sample Cha‐192 from the Murun alkaline complex. New data on the Raman spectra of LGMs obtained in this work show that the wavenumbers of the O—H stretching vibrations depend on the occupancies of the M 2 and M 3 sites coordinating with (OH) − groups. Cations other than Na + and Ti 4+ (mainly, Mg and Fe 3+ ) can play a significant role in the coordination of the X site occupied by (OH) − . Data on polarized Raman spectra of an oriented sample indicate that the OH groups having different local coordinations have similar orientations with respect to the crystal. The calculated measures of similarity (Δ) for lamprophyllite and ericssonite are identical (0.157 and 0.077 for the 2 M ‐ and 2 O ‐polytypes, respectively), which indicates that these minerals are crystal‐chemically isotypic and probably should be considered within the same mineral group by analogy to the other mineralogical groups which combine isotypic minerals.