Sulfite analogue of alloriite from Sacrofano, Latium, Italy: crystal chemitry and specific features of genesis

Chukanov N. V., Zubkova N. V., Pekov I. V., Giester G., Pushcharovsky D. Yu.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2021. V. 150. N 1. P. 48-62

https://doi.org/10.31857/S0869605521010044

Language: Russian 

Abstract

The chemical composition, IR spectroscopic characteristics, and crystal structure of the cancrinite group mineral with an afghanite-type framework, in which the SO₃^2– sulfite group is the dominant extra-framework anion, have been investigated. The studied mineral is hexagonal, space group P-62с; unit cell parameters are: a = 12.895(2), с = 21.276(4) Å, V = 3063.8(11) ų. A narrow channel, consisting of cancrinite cavities, hosts the …(Na_0.84Ca_0.16)–[(H₂O)_0.75Cl_0.23◊_0.02]–(Na_0.70 ◊_0.30)–[(H₂O)_0.75Cl_0.23◊_0.02]… chains. The rest of the extra-framework components populate the columns consisting of alternating liottite and cancrinite cages. In particular, the lyottite cage contains sulfate and sulfite groups with the latter dominating. The high content of SO₃^2– groups and the low content of SO₄^2– groups are confirmed by IR spectroscopy. The studied mineral is the SO₃^2–-dominant analogue of alloriite. The crystal chemical formula Na_2.53K₂Ca_2.73(Si₆Al₆O₂₄)(SO₃)_0.5[(SO₄)_0.53(SO₃)_0.47](OH)_0.99Cl_0.30×0.85H₂O (Z = 4) obtained as a result of structure refinement is close to the empirical one. The mechanisms of genesis of multilayer minerals of the cancrinite group are discussed.

Keywords: cancrinite-group minerals, afganite, alloriite, sulfite anion, crystal structure, infrared spectroscopy, Sacrofano paleovolcano