IMA 2020-H = Lazurite: validation as a mineral species and new data

[Marco E. Ciriotti]

Referenza:
▪ Sapozhnikov, A.N., Chukanov, N.V., Shendrik, R.Yu., Vigasina, M.F., Tauson, V.L., Lipko, S.V., Belakovskiy, D.I., Levitskii, V.I., Suvorova, L.F., Ivanova, L.A. (2021): Lazurite: validation as a mineral species and new data. Zapiski RMO, 150, 92-102.

Abstract:
The status of lazurite as a valid mineral species has been confirmed. The neotype specimen from the Malobystrinskoe gem lazurite deposit, Baikal Lake area has been investigated by means of electron microprobe analyses, analytical chemistry, ESR, IR, Raman, X-ray photoelectron spectroscopy, absorption and luminescence spectroscopy in UV and visible ranges and powder X-ray diffraction. The empirical formula of the neotype sample is (Na6.97Ca0.88К0.10)7.96[Si6.04Al5.96]12O24(SO4)1.09(S∙-3)0.55S2-0.05Cl0.04⋅0.72Н2О where S∙-3 is trisulfide radical anion which is a blue chromophore. The idealized formula Na7Ca(Al6Si6O24)(SO4)S∙-3⋅H2O has been approved by the IMA Commission on New Minerals, Nomenclature and Classification, proposal No. 20-H. The crystal structure of lazurite is characterized by commensurate and incommensurate modulations; the a parameter of the cubic sub-cell is equal to 9.087(3) Å. The neotype sample is slightly birefregent, with α' =1.523(2) and γ' = 1.525(2).