TY - JOUR

T1 - The solid solution in the system NaMgAl(SO4)3–KMgAl(SO4)3

AU - Jensen, Peter Grouleff

AU - Balic-Zunic, Tonci

AU - Nielsen, Ulla Gro

AU - Kofoed, Philip Miguel

N1 - Funding Information: UGN acknowledges funding from the Danish Council for Independent Research Science and Universe (Grant DFF-7014-00198). We acknowledge and thank Professor Woźniak and the Crystallochemistry Laboratory at the University of Warsaw for the possibility of using their thermogravimetric analysis (TGA) equipment for measurements. We acknowledge the open-access funding provided by the Royal Danish Library. The authors thank the three anonymous referees for their comments, which improved the text. Funding Information: UGN acknowledges funding from the Danish Council for Independent Research Science and Universe (Grant DFF-7014-00198). We acknowledge and thank Professor Woźniak and the Crystallochemistry Laboratory at the University of Warsaw for the possibility of using their thermogravimetric analysis (TGA) equipment for measurements. We acknowledge the open-access funding provided by the Royal Danish Library. The authors thank the three anonymous referees for their comments, which improved the text. Publisher Copyright: © 2023, The Author(s).

PY - 2023

Y1 - 2023

N2 - We synthesized six samples in the compositional field NaMgAl(SO4)3–KMgAl(SO4)3 in 20 mol% increments from pure Na to pure K compounds. We investigated them by Powder X-Ray diffraction, 23Na, and 27Al Nuclear Magnetic Resonance spectroscopy. The results confirm NaMgAl(SO4)3 as a unique phase identical to a presumed new mineral found in the fumaroles of Eldfell and Hekla volcanoes in Iceland. It tolerates less than 10 mol% K substitution for Na. There exists a compositional gap to approximately Na0.65K0.35MgAl(SO4)3 from where a solid solution extends to KMgAl(SO4)3. The mineral koryakite [NaKMg2Al2(SO4)6] is a member of the latter solid solution series. The crystal structures of all (Na,K)MgAl(SO4)3 phases are akin to NASICON (NA Super Ionic CONductor). NaMgAl(SO4)3 has R3 ¯ c symmetry and a disordered distribution of Mg and Al among the octahedral sites with only one unique site for the alkali atom. The members of the solid solution have R3 ¯ symmetry with ordered Mg–Al distribution and two unique alkali sites with different preferences for Na and K. In the crystal structure, the coordination of Na and/or K is trigonal antiprismatic, and these share bases with two octahedral Mg (Na) or Al (K) coordinations. These polyhedra are arranged in columns parallel to [001] and interconnected by SO4 tetrahedral groups. The alkali atoms from a column lie in the same (001) layers as the octahedrally coordinated atoms from the three neighboring rows. On the same level, parallel to (001), there are gaps in the other three neighboring columns forming channels containing Na+ or K+ ions.

AB - We synthesized six samples in the compositional field NaMgAl(SO4)3–KMgAl(SO4)3 in 20 mol% increments from pure Na to pure K compounds. We investigated them by Powder X-Ray diffraction, 23Na, and 27Al Nuclear Magnetic Resonance spectroscopy. The results confirm NaMgAl(SO4)3 as a unique phase identical to a presumed new mineral found in the fumaroles of Eldfell and Hekla volcanoes in Iceland. It tolerates less than 10 mol% K substitution for Na. There exists a compositional gap to approximately Na0.65K0.35MgAl(SO4)3 from where a solid solution extends to KMgAl(SO4)3. The mineral koryakite [NaKMg2Al2(SO4)6] is a member of the latter solid solution series. The crystal structures of all (Na,K)MgAl(SO4)3 phases are akin to NASICON (NA Super Ionic CONductor). NaMgAl(SO4)3 has R3 ¯ c symmetry and a disordered distribution of Mg and Al among the octahedral sites with only one unique site for the alkali atom. The members of the solid solution have R3 ¯ symmetry with ordered Mg–Al distribution and two unique alkali sites with different preferences for Na and K. In the crystal structure, the coordination of Na and/or K is trigonal antiprismatic, and these share bases with two octahedral Mg (Na) or Al (K) coordinations. These polyhedra are arranged in columns parallel to [001] and interconnected by SO4 tetrahedral groups. The alkali atoms from a column lie in the same (001) layers as the octahedrally coordinated atoms from the three neighboring rows. On the same level, parallel to (001), there are gaps in the other three neighboring columns forming channels containing Na+ or K+ ions.

KW - (Na,K)MgAl(SO)

KW - Anhydrous sulfates

KW - Fumarolic minerals

KW - Koryakite

KW - NASICON-type structure

U2 - 10.1007/s00269-023-01259-0

DO - 10.1007/s00269-023-01259-0

M3 - Journal article

AN - SCOPUS:85177748411

VL - 50

JO - Physics and Chemistry of Minerals

JF - Physics and Chemistry of Minerals

SN - 0342-1791

IS - 4

M1 - 35

ER -