Crystal-chemistry of micas belonging to the yangzhumingite-fluorophlogopite and phlogopite-fluorophlogopite series from
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ORIGINAL PAPER
Crystal‑chemistry of micas belonging to the yangzhumingite‑fluorophlogopite and phlogopite‑fluorophlogopite series from the Apuan Alps (northern Tuscany, Italy) Maria Lacalamita1 · Emanuela Schingaro1 · Ernesto Mesto1 · Federica Zaccarini2 · Cristian Biagioni3 Received: 7 August 2020 / Accepted: 7 October 2020 © The Author(s) 2020
Abstract The present work reports the crystal-chemical characterization of micas from the Monte Arsiccio and Buca della Vena mines (Apuan Alps, Italy) through electron microprobe analysis, single-crystal X-ray diffraction, and Raman spectroscopy. The sample from the Monte Arsiccio mine can be classified as an intermediate member of the yangzhumingite-f luorophlogopite series, with average crystal-chemical formula (K0.85Na0.01Ba0.09)Σ=0.95(Mg2.11Fe2+0.23Fe3+0.11Cr3+0.01Al0.20Ti0.04☐0.30)Σ=3.00(Si3.20Al0.80)Σ=4.00O10.00F1.90Cl0.02(OH)0.08. Unitcell parameters are a ~ 5.30, b ~ 9.18, c ~ 10.14 Å, β ~ 100.12°, V ~ 486.22 Å3, corresponding to the 1M polytype. Structure refinements, performed in C2/m space group, converged to R1 = 3.54 and 4.46% and provided Mg plus Fe occupancy in the range 86–94% for the octahedral M1 and M2 sites. Raman spectroscopy shows very weak bands in the OH stretching region at ~ 3690 and 3580 cm−1. The sample from the Buca della Vena mine has been identified as an (OH)-rich fluorophlogopite, with average crystal-chemical formula (K0.84Na0.02Ca0.01)Σ=0.87(Mg2.12Fe2+0.55Fe3+0.10Al0.18☐0.05)Σ=3.00(Si2.99Al1.01)Σ=4.00O10.00F1.02Cl0.09(OH) 3 0.89. Its unit-cell parameters are a ~ 5.33, b ~ 9.22, c ~ 10.23 Å, β ~ 100.09°, V ~ 494.39 Å . Structure refinements gave good R1 values (3.27 and 4.37%) and revealed octahedral occupancy of 82–84% Mg and 16–18% Fe. Strong Raman signals at ~ 3702 cm−1 and 3595 cm−1 were observed in the OH stretching region. The findings allow to better understand not only the mineralogy of the Apuan Alps but, more generally, the crystal chemical details of intermediate dioctahedral-trioctahedral mica belonging to the yanzhumingite-fluorophlogopite series. Keywords Yangzhumingite-fluorophlogopite series · Phlogopite-fluorophlogopite series · Crystal-chemistry · Monte Arsiccio · Buca della Vena · Apuan Alps
Introduction Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00269-020-01118-2) contains supplementary material, which is available to authorized users. * Maria Lacalamita [email protected] 1
Dipartimento di Scienze della Terra e Geoambientali, Università degli Studi di Bari ALDO MORO, via Orabona 4, 70125 Bari, Italy
2
Department of Applied Geological Sciences and Geophysics, University of Leoben, Peter Tunner Str. 5, 8700 Leoben, Austria
3
Dipartimento di Scienze della Terra, Università di Pisa, via Santa Maria 53, 56126 Pisa, Italy
Yangzhumingite, ideally K Mg 2.5 Si 4 O 10 F 2 , is a tetrasilicic potassium fluor-mica found in few localities worldwide. The first natural occurrence of this very rare mineral was reported in a metamorphosed carbonate roc
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