TY - JOUR

T1 - Single-crystal X-ray diffraction and IR-spectroscopy studies of potassium-deficient fluorapophyllite-(K)

AU - Seryotkin, Yurii V.

AU - Kupriyanov, Igor N.

AU - Ignatov, Mark A.

N1 - We thank P. Vignola and the anonymous reviewer for their comprehensive remarks. This study is supported by the Russian Science Foundation (grant # 22-27-00235). The chemical analyses were carried out at the Analytical Center for Multi-Elemental and Isotope Research (Sobolev Institute of Geology and Mineralogy, Novosibirsk, Russia). X-ray experiments were done using the equipment of Research and Education Centre “Molecular Design and Ecologically Safe Technologies” at NSU. I.N. Kupriyanov’s investigation of aphophyllite by infrared absorption spectroscopy was supported by the Russian Science Foundation under grant # 22-17-00005.

PY - 2023/3

Y1 - 2023/3

N2 - Three samples of fluorapophyllite-(K) with different cation composition were studied by the X-ray diffraction and IR-spectroscopy methods. The samples (K0.72(NH4)0.20)Σ0.92Na0.08 Ca4[Al0.04Si7.96O20]F·8H2O from Nidym and K0.87Na0.06 Ca4[Si8O20]F·8H2O from Akhaltsykhe localities are characterized by the deficiency of large cations K+ and (NH4)+ in the A site; the chemical composition of Talnakh sample (K0.94(NH4)0.06)Σ1.00 Ca4[Si8O20]F·8H2O is close to the stoichiometric one. The large cations deficiency in the structure of Nidym and Akhaltsykhe samples is compensated by the presence of medium-sized Na+ cations, located 1.12–1.31 Å away from the A position. The planar coordination of Na is formed by four H2O molecules. The occurrence of ammonium ions is found for the Nidym and Talnakh samples and their concentrations are estimated from the IR spectra and structure refinement. Polarized infrared measurements performed for fluorapophyllite-(K) samples oriented along the c-axis reveal pleochroic behavior of the OH absorption bands. The observed pleochroism is explained in terms of absorption from two OH vectors of the H2O molecules in the crystal structure.

AB - Three samples of fluorapophyllite-(K) with different cation composition were studied by the X-ray diffraction and IR-spectroscopy methods. The samples (K0.72(NH4)0.20)Σ0.92Na0.08 Ca4[Al0.04Si7.96O20]F·8H2O from Nidym and K0.87Na0.06 Ca4[Si8O20]F·8H2O from Akhaltsykhe localities are characterized by the deficiency of large cations K+ and (NH4)+ in the A site; the chemical composition of Talnakh sample (K0.94(NH4)0.06)Σ1.00 Ca4[Si8O20]F·8H2O is close to the stoichiometric one. The large cations deficiency in the structure of Nidym and Akhaltsykhe samples is compensated by the presence of medium-sized Na+ cations, located 1.12–1.31 Å away from the A position. The planar coordination of Na is formed by four H2O molecules. The occurrence of ammonium ions is found for the Nidym and Talnakh samples and their concentrations are estimated from the IR spectra and structure refinement. Polarized infrared measurements performed for fluorapophyllite-(K) samples oriented along the c-axis reveal pleochroic behavior of the OH absorption bands. The observed pleochroism is explained in terms of absorption from two OH vectors of the H2O molecules in the crystal structure.

KW - Apophyllite group

KW - Crystal structure

KW - Hydrogen bonds

KW - IR spectroscopy

KW - Potassium-deficient fluorapophyllite-(K)

KW - X-ray diffraction

UR - https://www.scopus.com/inward/record.url?eid=2-s2.0-85147497447&partnerID=40&md5=26747ecf45fa81ff20d6d82bbb0f3164

UR - https://www.mendeley.com/catalogue/a14a1cd3-e6e5-3020-9d03-03a672e20cc6/

U2 - 10.1007/s00269-022-01229-y

DO - 10.1007/s00269-022-01229-y

M3 - Article

VL - 50

JO - Physics and Chemistry of Minerals

JF - Physics and Chemistry of Minerals

SN - 0342-1791

IS - 1

M1 - 6

ER -