TY - JOUR

T1 - The crystal structure of magnesian halotrichite, (Fe,Mg)Al2(SO4)4·22H2O: hydrogen bonding, geometrical parameters and structural complexity

AU - Zhitova, E.s.

AU - Sheveleva, R.m.

AU - Zolotarev, A.a.

AU - Krivovichev, S.v.

AU - Shilovskikh, V.v.

AU - Nuzhdaev, A.a.

AU - Nazarova, M.a.

PY - 2023/8/13

Y1 - 2023/8/13

N2 - The crystal structure of magnesian halotrichite has been refined for two samples collected as white efflorescences from the surface of geothermal fields associated with the Koshelevsky (sample VK4-09) and Centralny Semyachik (sample SC2-20) volcanoes (both Kamchatka peninsula, Russia). Halotrichite and its Mg-rich varieties are common products of the acid leaching of rocks, both volcanic and technogenic. The crystal structures of two halotrichite crystals were refined in the P21 /n space group (vs. P21 /c used previously) with the unit-cell parameters a = 6.1947(2)/ 6.1963(5) Å, b = 24.2966(8)/ 24.2821(14) Å, c = 21.0593(8)/ 21.063(2) Å, β = 96.512(4)/ 96.563(9) º, V = 3149.2(2)/ 3148.3(5) Å3, Z = 4 to R1 = 0.055 and 0.067 for 5673 and 3936 reflections with I > 2σI reflections, respectively. The crystal structure consists of isolated Al(H2 O)6 octahedra, SO4 tetrahedra, H2 O molecules and [X(SO4)(H2 O)5 ]0 clusters (X = Fe, Mg). The chemical analyses of both samples show their enrichment of Mg at the Fe2+ site. The analysis of geometrical parameters of the crystal structures of halotrichite and its Mg-analogue pickeringite suggests that the localization of O atoms carried out in this work is more accurate and the single-crystal X-ray diffraction data for the first time allowed localization of hydrogen atom positions. The refined number of H2 O molecules agrees with the ideal chemical formula. The crystal structure complexity of halotrichite is estimated as IG,total = 2305 bits/cell, which belongs to the family of very complex mineral structures. The contribution of hydrogen bonding system plays a significant role in the overall bonding scheme and the overall complexity of the crystal structure, increasing the Shannon information amount more than twice from IG,total(noH) = 988 bits/cell (no hydrogen atoms) to IG,total = 2305 bits/cell (all atoms including hydrogen). The comparative distribution of halotrichite relative to other Fe-Al hydrated sulfates from the standpoint of structural complexity is considered.

AB - The crystal structure of magnesian halotrichite has been refined for two samples collected as white efflorescences from the surface of geothermal fields associated with the Koshelevsky (sample VK4-09) and Centralny Semyachik (sample SC2-20) volcanoes (both Kamchatka peninsula, Russia). Halotrichite and its Mg-rich varieties are common products of the acid leaching of rocks, both volcanic and technogenic. The crystal structures of two halotrichite crystals were refined in the P21 /n space group (vs. P21 /c used previously) with the unit-cell parameters a = 6.1947(2)/ 6.1963(5) Å, b = 24.2966(8)/ 24.2821(14) Å, c = 21.0593(8)/ 21.063(2) Å, β = 96.512(4)/ 96.563(9) º, V = 3149.2(2)/ 3148.3(5) Å3, Z = 4 to R1 = 0.055 and 0.067 for 5673 and 3936 reflections with I > 2σI reflections, respectively. The crystal structure consists of isolated Al(H2 O)6 octahedra, SO4 tetrahedra, H2 O molecules and [X(SO4)(H2 O)5 ]0 clusters (X = Fe, Mg). The chemical analyses of both samples show their enrichment of Mg at the Fe2+ site. The analysis of geometrical parameters of the crystal structures of halotrichite and its Mg-analogue pickeringite suggests that the localization of O atoms carried out in this work is more accurate and the single-crystal X-ray diffraction data for the first time allowed localization of hydrogen atom positions. The refined number of H2 O molecules agrees with the ideal chemical formula. The crystal structure complexity of halotrichite is estimated as IG,total = 2305 bits/cell, which belongs to the family of very complex mineral structures. The contribution of hydrogen bonding system plays a significant role in the overall bonding scheme and the overall complexity of the crystal structure, increasing the Shannon information amount more than twice from IG,total(noH) = 988 bits/cell (no hydrogen atoms) to IG,total = 2305 bits/cell (all atoms including hydrogen). The comparative distribution of halotrichite relative to other Fe-Al hydrated sulfates from the standpoint of structural complexity is considered.

KW - crystal structure

KW - halotrichite

KW - hot spring

KW - pickeringite

KW - structural complexity

KW - sulfate

UR - https://www.mendeley.com/catalogue/44c1f1c2-68e1-39af-aec6-00c811e5cf95/

U2 - 10.3190/jgeosci.372

DO - 10.3190/jgeosci.372

M3 - Article

VL - 68

SP - 163

EP - 178

JO - Journal of Geosciences

JF - Journal of Geosciences

SN - 1802-6222

IS - 2

ER -