Eight mineral species in one crystal: unique zonation of polychrome tourmaline from the Krutaya vein (Malkhan pegmatite feld, Transbaikalia, Russia)

A.V. Kasatkin, О.S. Vereshchagin, L.A. Gorelova, D.I. Belakovskiy

A unique unusually Mn-rich concentrically zoned polychrome crystal from the cavity of granite pegmatite of the Krutaya vein within the Malkhan pegmatite feld (Transbaikalia) is studied. It consists of six valid and two potentially new mineral species of the tourmaline supergroup. The paper provides the detailed physical, chemical and crystallographic characteristics of minerals. A Mn-richest (up to 9.6 wt. % MnO) dark brown core of the crystal is composed of fuor-tsilaisite, princivalleite and a Mn2+-F-analog of foitite. A greenish yellow intermediate zone consists of Mn-rich fuor-elbaite and darrellhenryite and is followed by a Mn-poor pink zone composed of fuor-rossmanite, rossmanite and their O2–analog. A yellowish green peripheral zone consists of late-generation Mn-bearing fuor-elbaite. The Mn content decreases, while the Li + Al content increases from the center of the dark brown zone to the margin of the crystal approximately to the middle of the pink zone, where the evolution of the tourmaline composition is inverted and this trend becomes opposite. The crystal structure of fuor-tsilaisite is refned on a single crystal extracted from this specimen, R1 = 2.4 %. The mineral is trigonal, space group R3m, a = 15.9595(1), c = 7.14164(7) Å, V = 1575.31(3) Å3, Z = 3.

Keywords: crystal zonation, polychrome crystal, tourmaline, fuor-elbaite, fuor-tsilaisite, princivalleite, darrellhenryite, fuor-rossmanite, crystal structure, Krutaya vein, Malkhan pegmatite feld.

Funding. The laboratory studies were carried out at the Research Park of St. Petersburg State University in the “X-ray Diffraction Centre”.

Acknowledgements. We are grateful to Igor V. Pekov, Elena V. Belogub and Irina Yu. Melekestseva for constructive and critical comments, which allowed us to improve the manuscript. Mikhail Yu. Anosov kindly provided the polychrome crystal. We thank Kontstantin A. Bukholtsev, director of the company “Technologiya” and its chief geologist Petr F. Ivanov for detailed information on the locality. Vasiliy O. Yapaskurt and Fabrizio Nestola assisted in analytical works and Maria D. Milshina helped with the photography of the samples and the preparation of the fgures.

Confict of interest. The authors declare that they have no conficts of interest.

Author contribution. A.V. Kasatkin – conceptualization, investigation; A.V. Kasatkin, O.S. Vereshchagin, L.A. Gorelova, D.I. Belakovskiy – analytical/experimental works; A.V. Kasatkin, O.S. Vereshchagin, L.A. Gorelova – writing – original draft, visualization, writing – review & editing. All the authors approved the fnal version of the manuscript prior to publication.

For citation: Kasatkin A.V., Vereshchagin O.S., Gorelova L.A., Belakovskiy D.I. Eight mineral species in one crystal: unique zonation of polychrome tourmaline from the Krutaya vein (Malkhan pegmatite feld, Transbaikalia, Russia). Mineralogy, 10(2), 5–25. DOI: 10.35597/2313-545X-2024-10-2-1

Received 01.04.2024, revised 03.04.2024, accepted 18.04.2024

 

MINERALIGY 2 2024