TY - JOUR

T1 - Heat-Induced Mn2+ and Fe2+ Oxidation in Heterophyllosilicates: Kupletskite and Kupletskite-(Cs)

AU - Zhitova, Elena S.

AU - Zolotarev, Andrey A.

AU - Sheveleva, Rezeda M.

AU - Shendrik, Roman Yu.

AU - Hawthorne, Frank C.

AU - Nuzhdaev, Anton A.

AU - Vlasenko, Natalia S.

AU - Kaneva, Ekaterina V.

AU - Yakovenchuk, Victor N.

PY - 2025/5/30

Y1 - 2025/5/30

N2 - The crystal–chemical behavior of two layered titanosilicate minerals with porous crystal structures, kupletskite, K2NaMn72+Ti2(Si4O12)2O2(OH)4F, and kupletskite-(Cs), Cs2NaMn72+Ti2(Si4O12)2O2(OH)4F, was investigated under high-temperature conditions using single-crystal and powder X-ray diffraction; infrared and optical absorption spectroscopy and electron-microprobe analysis. Both minerals undergo topotactic transformation to dehydroxylated and oxidized high-temperature (HT) modifications at temperature above 500 °C while maintaining the basic bond topology of the astrophyllite structure-type. The high-temperature structures show contraction of the unit-cell parameters similar to that of Fe2+-dominant astrophyllite, indicating that Mn2+ oxidizes along with Fe2+ in M(2)–M(4) sites. The oxidation of Mn2+ is confirmed by the increase of the Mn3+-related absorption (in optical spectra) that is inversely correlated with the intensity of O–H bands in the infrared spectra. The Fe,Mn-oxidation is also evident by the contraction of the M(2), M(3), and M(4)O6 octahedra. The M(1)–O bond length increases slightly, indicating a preference for mono- and divalent cations to occupy the M(1) site in the heated structure; this may be due to site-selective oxidation and/or migration of unoxidized cations (as previously shown for lobanovite) to this site. The role of extra framework A-site cations (K, Cs) in thermal expansion of these minerals is discussed.

AB - The crystal–chemical behavior of two layered titanosilicate minerals with porous crystal structures, kupletskite, K2NaMn72+Ti2(Si4O12)2O2(OH)4F, and kupletskite-(Cs), Cs2NaMn72+Ti2(Si4O12)2O2(OH)4F, was investigated under high-temperature conditions using single-crystal and powder X-ray diffraction; infrared and optical absorption spectroscopy and electron-microprobe analysis. Both minerals undergo topotactic transformation to dehydroxylated and oxidized high-temperature (HT) modifications at temperature above 500 °C while maintaining the basic bond topology of the astrophyllite structure-type. The high-temperature structures show contraction of the unit-cell parameters similar to that of Fe2+-dominant astrophyllite, indicating that Mn2+ oxidizes along with Fe2+ in M(2)–M(4) sites. The oxidation of Mn2+ is confirmed by the increase of the Mn3+-related absorption (in optical spectra) that is inversely correlated with the intensity of O–H bands in the infrared spectra. The Fe,Mn-oxidation is also evident by the contraction of the M(2), M(3), and M(4)O6 octahedra. The M(1)–O bond length increases slightly, indicating a preference for mono- and divalent cations to occupy the M(1) site in the heated structure; this may be due to site-selective oxidation and/or migration of unoxidized cations (as previously shown for lobanovite) to this site. The role of extra framework A-site cations (K, Cs) in thermal expansion of these minerals is discussed.

KW - Cs

KW - Fe oxidation

KW - Mn oxidation

KW - crystal structure

KW - kupletskite

KW - kupletskite-(Cs)

KW - mineral

KW - porous material

KW - spectroscopy

KW - titanosilicate

UR - https://www.mendeley.com/catalogue/eb3d1f07-f08e-35e4-9ed2-1870204cf32f/

U2 - 10.3390/min15060587

DO - 10.3390/min15060587

M3 - Article

VL - 15

JO - Minerals

JF - Minerals

SN - 2075-163X

IS - 6

M1 - 587

ER -