TY - JOUR

T1 - Reversible hydration/dehydration and thermal expansion of euchlorine, ideally KNaCu3O(SO4)3

AU - Siidra, Oleg I.

AU - Borisov, Artem S.

AU - Lukina, Evgeniya A.

AU - Depmeier, Wulf

AU - Platonova, Natalia V.

AU - Colmont, Marie

AU - Nekrasova, Diana O.

PY - 2019/4/1

Y1 - 2019/4/1

N2 - Anhydrous alkali copper sulfates constitute the most abundant group of mineral species from the Second Scoria Cone of the Great Tolbachik Fissure Eruption (1975–1976), a location being renowned for its great mineral diversity. Euchlorine, ideally KNaCu 3O(SO 4) 3, is the prevalent mineral in the hot sulfate-rich zones of the fumaroles. In this work, its thermal expansion and hydration/dehydration behavior have been studied. The results of a structure refinement from new single-crystal diffraction data are also reported, and a description of the structure based on anion-centered coordination polyhedra is given. The strongly anisotropic character of the thermal expansion of euchlorine remains essentially unchanged up to its decomposition. The strongest α 11 expansion is observed approximately perpendicular to the alkali interlayer of the structure, whereas the minimal α 22 and α 33 thermal expansion coefficients are parallel to the plane of {Cu 3O(SO 4) 3} 2− layers. Hydration experiments controlled by X-ray powder diffraction reveal a very complex behavior with multicomponent phase formation. Remarkably, upon heating stepwise dehydration occurs, whereby the complex mixture of hydrated sulfates gradually reverses and becomes again essentially single-phased anhydrous euchlorine.

AB - Anhydrous alkali copper sulfates constitute the most abundant group of mineral species from the Second Scoria Cone of the Great Tolbachik Fissure Eruption (1975–1976), a location being renowned for its great mineral diversity. Euchlorine, ideally KNaCu 3O(SO 4) 3, is the prevalent mineral in the hot sulfate-rich zones of the fumaroles. In this work, its thermal expansion and hydration/dehydration behavior have been studied. The results of a structure refinement from new single-crystal diffraction data are also reported, and a description of the structure based on anion-centered coordination polyhedra is given. The strongly anisotropic character of the thermal expansion of euchlorine remains essentially unchanged up to its decomposition. The strongest α 11 expansion is observed approximately perpendicular to the alkali interlayer of the structure, whereas the minimal α 22 and α 33 thermal expansion coefficients are parallel to the plane of {Cu 3O(SO 4) 3} 2− layers. Hydration experiments controlled by X-ray powder diffraction reveal a very complex behavior with multicomponent phase formation. Remarkably, upon heating stepwise dehydration occurs, whereby the complex mixture of hydrated sulfates gradually reverses and becomes again essentially single-phased anhydrous euchlorine.

KW - Euchlorine

KW - Evolution of minerals

KW - Exhalative minerals

KW - Reversible hydration/dehydration

KW - Sulfates

KW - Thermal expansion

KW - Tolbachik volcano

KW - X-ray diffraction

KW - CRYSTAL-STRUCTURE

KW - KAMCHATKA

KW - TETRAHEDRA

KW - REFINEMENT

KW - TOLBACHIK VOLCANO

KW - Reversible hydration

KW - dehydration

KW - HYDRATED SULFATE MINERALS

UR - http://www.scopus.com/inward/record.url?scp=85056428357&partnerID=8YFLogxK

U2 - 10.1007/s00269-018-1011-9

DO - 10.1007/s00269-018-1011-9

M3 - Article

AN - SCOPUS:85056428357

VL - 46

SP - 403

EP - 416

JO - Physics and Chemistry of Minerals

JF - Physics and Chemistry of Minerals

SN - 0342-1791

IS - 4

ER -