https://doi.org/10.3390/cryst12030377
“In this study, natural tinaksite (K2Ca2NaTi[Si7O18OH]O) and tokkoite (K2Ca4[Si7O18OH](OH,F)) collected in charoite rocks of the Murun alkaline massif (Siberia, Russia) were examined by X-ray diffraction and optical and vibrational spectroscopic methods. A comparative analysis of the experimental diffraction patterns with respect to the calculated X-ray powder diffraction patterns was carried out for tinaksite and tokkoite powders. The shift in the diffraction peaks of tinaksite is explained by the smaller values of the unit cell parameters a and b as compared with those of tokkoite. A similar shift of the peaks is also observed in the Raman and infrared absorption spectra; however, this feature is explained by the difference in the chemical composition of the minerals. The shoulder in the absorption spectra at about 800 nm in tinaksite and 700 nm in tokkoite corresponds to the presence of Mn2+ and Fe3+ absorption bands, the presence of which determines the color of tinaksite and tokkoite. The luminescence band with a maximum at about 540–550 nm in the photoluminescence spectra is related to Mn2+ centers, while an additional band at about 610 nm can be associated with Ti3+ centers in tinaksite. The intensity of the Fe3+ ESR signal increases in both samples after heating, while the intensities of the bands associated with OH groups decrease in tinaksite and tokkoite. This characteristic is the result of iron oxidation and dehydrogenation reaction.”
“The X-ray powder diffraction data of the studied samples were collected at room temperature with a Bruker D8 ADVANCE (Bruker AXS, Berlin, Germany) powder diffractometer (Cu Kα radiation, 40 kV, 40 Ma) and linear VANTEC detector. The samples for measurement were prepared by packing and leveling the powder in a special cuvette. Profiles were obtained between 3° and 120° 2θ. The step size of 2θ was 0.02°, and the counting time was 4 s per step. The measured patterns were used without any corrections or other processing. Diffraction patterns were analyzed using the EVA V4.2.1 software suite [22] (Bruker AXS, Madison, WI, USA). To establish the features of powder diffraction patterns and compare them with those previously obtained, the Powder Diffraction File (PDF-2, Release 2007) database, maintained and updated by the International Center for Diffraction Data [23,24], was used. In this study, the VESTA (version 4.3.0) software [20] was used to simulate the X-ray diffraction patterns of tinaksite and tokkoite using the crystal structure models of [18,21]. The unit cell parameters of the studied samples were determined by the Rietveld method using TOPAS 4.2 (Bruker AXS, Berlin, Germany) [25]. Refinements were stable and gave relatively low R-factors (4.7 and 5.1% for tinaksite and tokkoite, respectively). Pseudo-Voigt line shapes were used for the peaks. A three-parameter 2nd order polynomial function was used for the background. The measured patterns were used without any corrections or other processing; Lorentz polarization, absorption, and sample displacement corrections were applied to the calculated patterns.”
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3.1. X-ray Powder Diffraction

a (Å) | b (Å) | c (Å) | α (°) | β (°) | γ (°) | Sp. Gr. | Source |
---|---|---|---|---|---|---|---|
Tinaksite | |||||||
10.371 (6) | 12.167 (6) | 7.060 (5) | 90.91 (2) | 99.37 (3) | 92.79 (3) | P1¯�1¯ | This work |
10.375 (2) | 12.190 (2) | 7.057 (1) | 90.75 (3) | 99.25 (3) | 92.81 (3) | P1¯�1¯ | [18] |
10.370 (1) | 12.162 (1) | 7.057 (1) | 90.89 (1) | 99.20 (1) | 92.80 (1) | P1¯�1¯ | [18] |
10.361 (2) | 12.153 (2) | 7.044 (1) | 90.79 (2) | 99.22 (2) | 92.83 (2) | P1¯�1¯ | [31] |
10.350 | 12.170 | 7.050 | 91.00 | 99.33 | 92.50 | P1¯�1¯ | PDF 00-018-1382 |
10.369 | 12.177 | 7.052 | 90.00 | 99.00 | 92.00 | P1¯�1¯ | PDF 00-054-0646 |
10.350 | 12.170 | 7.050 | 91.00 | 99.33 | 92.50 | P1 | PDF 01-072-1823 |
10.377 | 12.166 | 7.059 | 90.91 | 99.30 | 92.76 | P1¯�1¯ | PDF 01-071-1758 |
Tokkoite | |||||||
10.436 (5) | 12.474 (7) | 7.085 (4) | 89.98 (3) | 99.50 (3) | 92.89 (3) | P1¯�1¯ | This work |
10.423 (1) | 12.492 (1) | 7.116 (1) | 89.89 (1) | 99.69 (1) | 92.95 (1) | P1¯�1¯ | [18] |
10.424 (1) | 12.477 (1) | 7.113 (1) | 89.88 (1) | 99.68 (1) | 92.99 (1) | P1¯�1¯ | [18] |
10.423 (1) | 12.462 (1) | 7.106 (1) | 89.98 (1) | 99.68 (1) | 92.95 (1) | P1¯�1¯ | [18] |
10.370 | 25.390 | 7.270 | 91.67 | 100.66 | 92.09 | P1¯�1¯ | PDF 00-040-0517 |
10.438 | 12.511 | 7.112 | 89.92 | 99.75 | 92.89 | P1¯�1¯ | PDF 01-079-1981 |
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