Crystal structure and hydrogen bond system of melanterite

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Marco E. Ciriotti
Messaggi: 24897
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Crystal structure and hydrogen bond system of melanterite

Messaggio da Marco E. Ciriotti » mar 03 apr, 2018 9:59

Referenza:
▪ Mauro, D., Biagioni, C., Pasero, M. (2018): Crystal-chemistry of sulfates from Apuan Alps (Tuscany, Italy). I. Crystal structure and hydrogen bond system of melanterite, Fe(H2O)6(SO4)•H2O. Periodico di Mineralogia, 87, 89-96.

Abstract:
Melanterite, ideally Fe(H2O)6SO4·H2O, from the pyrite + iron oxide ore deposit of Fornovolasco (Apuan Alps, Tuscany, Italy) has been fully characterized through electron microprobe analysis, micro-Raman spectroscopy, and X-ray diffraction. Melanterite occurs as cm-sized greenish fibrous efflorescences on pyrite or rare pseudo-octahedral colorless crystals, up to 5 mm in size. Electron microprobe analysis (in wt% - average of ten spot analyses normalized to 100 wt% without H2O) gave: SO3 52.98, FeO 45.53, MgO 1.49, sum 100.00. Assuming the occurrence of 7 H2O groups per formula unit, the chemical formula can be written as (Fe0.95Mg0.06)Σ1.01(SO4)·7H2O. The Raman spectrum of melanterite is characterized by bending and stretching modes of (SO4) and H2O groups. Melanterite crystallizes in the space group P21/c, with unit-cell parameters a = 14.0751(8), b = 6.5014(4), c = 11.0426(6) Å, β = 105.632(3)°, V = 973.11(10) Å3, Z = 4. The crystal structure of melanterite has been refined down to R1 = 0.024 on the basis of 3457 reflections with Fo > 4σ(Fo) and 179 refined parameters. It can be described as formed by undulating layers showing the alternation, along a, of SO4 groups and Fe-centered octahedra coordinated by H2O groups. The occurrence of a complex hydrogen bond system plays a fundamental role in the crystal structure of melanterite.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 24897
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Re: Crystal structure and hydrogen bond system of melanterite

Messaggio da Marco E. Ciriotti » mer 04 apr, 2018 11:37

La formula della melanterite, come ben dimostra il lavoro strutturale di cui al precedente messaggio, può essere espressa meglio con:
Fe2+(H2O)6(SO4)·H2O.

Idem per le specie isostrutturali del gruppo:
Alpersite Mg(H2O)6(SO4)·H2O
Bieberite Co(H2O)6(SO4)·H2O
Boothite Cu2+(H2O)6(SO4)·H2O
Mallardite Mn2+(H2O)6(SO4)·H2O
Zincmelanterite Zn(H2O)6(SO4)·H2O
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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