# Identification of anhydrous CaCl2 and KCaCl3 in natural inclusions by Raman spectroscopy

Svetlana Grishina, Peter Koděra, Lucas M. Uriarte, Jean Dubessy, Aleksandr Oreshonkov, Sergey Goryainov, František Šimko, Igor Yakovlev, Evgenii M. Roginskii

► To cite this version:

Svetlana Grishina, Peter Koděra, Lucas M. Uriarte, Jean Dubessy, Aleksandr Oreshonkov, et al. Identification of anhydrous CaCl2 and KCaCl3 in natural inclusions by Raman spectroscopy. Chemical Geology, 2018, Chemical Geology, 493, pp.532-543. 10.1016/j.chemgeo.2018.07.017. hal-04474404

HAL Id: hal-04474404

https://lilloa.hal.science/hal-04474404v1

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# Identification of anhydrous CaCl₂ and KCaCl₃ in natural inclusions by Raman spectroscopy

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GRISHINA Svetlana¹, KODĚRA Peter², URIARTE Lucas M.³, DUBESSY Jean³,

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ORESHONKOV Aleksandr⁴,⁵, GORYAINOV Sergey¹, ŠIMKO František⁶, YAKOVLEV Igor¹.

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ROGINSKII Evgenii M.⁷

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1: Sobolev Institute of Geology and Mineralogy Siberian Branch of the Russian Academy of Sciences, Koptuyg Avenue 3, Novosibirsk 630090, Russia

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2: Department of Economic Geology, Comenius University, Faculty of Natural Sciences, Ilkovičova 6, 842 15 Bratislava, Slovakia

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3: Université de Lorraine, CNRS, CREGU, GeoRessources laboratory (UMR 7359), Vandoeuvre-lès-Nancy, BP-70239, F-54506, France

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4: Kirensky Institute of Physics, Federal Research Center KSC SB RAS Akademgorodok 50/38, Krasnoyarsk 660036, Russia

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5: Siberian Federal University, Svobodniy 79, Krasnoyarsk 660079, Russia

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6: Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, 845 36 Bratislava, Slovakia

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7: Ioffe Institute, St. Petersburg 194021, Russia

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Keywords: polymorphs CaCl₂, Raman spectra, magma-salt interaction, chlorocalcite, daughter mineral, *ab initio* calculations

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Author for checking the proof: Koděra Peter

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e-mail peter.kodera@gmail.com

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## ABSTRACT

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Anhydrous chlorides - CaCl₂, and KCaCl₃ (chlorocalcite) were identified as mineral inclusions in halite from the Siberian Large Igneous Province at the contact of magmatic intrusions and evaporates. Chlorocalcite was also found as daughter mineral in polyphase hypersaline inclusions. While Raman spectra of KCaCl₃ (chlorocalcite) in natural inclusions are similar to spectra of synthetic analogue, the Raman spectra of natural CaCl₂ do not correspond to the published Raman spectra of synthetic CaCl₂. Simulations of Raman spectra using *ab initio* density-functional theory (DFT) allowed us to calculate the spectra of individual polymorphs of CaCl₂ and to discriminate anhydrous CaCl₂ phases in natural inclusions and synthetic CaCl₂. In
the spectrum of the *Pbcn* polymorph of CaCl₂ twelve different peaks could be identified at 74, 95, 99, 107, 124, 158, 164, 179, 212, 236, 244, 256 cm⁻¹ in contrast to five peaks in the spectrum of the *Pnnm* polymorph of CaCl₂ at 115, 157, 160, 211 and 252 cm⁻¹. Naturally occurring CaCl₂ in inclusions in halite consist of Pbcn polymorph only, which probably results from a mechanical stress on cooling from magmatic to ambient temperatures. However, the Raman spectra of the synthetic CaCl₂ corresponds to the *Pnnm* phase with small contributions of the *Pbcn* phase.

Raman spectra of synthetic KCaCl₃ with main peaks at 58, 67, 90, 97, 133, 139, 147, 193 cm⁻¹ agrees well with the spectra of chlorocalcite in the natural inclusions. Positions of each atom in the KCaCl₃ structure were refined using the density-functional theory. There are no imaginary phonon modes for the optimized structure, indicating that the structure of KCaCl₃ is stable. Calculated Raman spectrum is in a good agreement with the Raman spectrum of synthetic and natural KCaCl₃ samples.

## 1. INTRODUCTION

Highly saline paleofluids and molten salts are reported from a wide range of geological environments (e.g. Roedder, 1992). It is widely recognized, that chloride-rich brines play an important role in transport and precipitation of metals as well as gems to form economic mineralizations in diverse geological settings, but especially in magmatic-hydrothermal and metamorphic systems (Reyf & Bazheyev, 1977; Kamenetsky et al., 2002; Newton and Manning, 2010; Lecumberri-Sanchez et al., 2015; Giuliani et al., 2017).

Fluid inclusions provide the best available means to characterize the physical and chemical properties of fluids in fossil hydrothermal systems (Naumov et al., 1990, Andreeva et al., 1998, Bodnar et al., 2014). One of the most important high-salinity hydrothermal systems is the geochemical system NaCl-KCl-CaCl₂-H₂O that often includes deep-crustal and upper mantle fluids. Chemical analysis of associated fluid inclusions and their daughter minerals can help to understand the connection between magmatic processes and the composition of magmatic-hydrothermal fluids (Audetat et al., 2008). The high salinity fluids and melts, trapped in multiphase fluid inclusions, often host one or more chloride daughter minerals at ambient temperature due to the precipitation of solid salts on cooling of the inclusions from trapping temperatures. Chloride daughter minerals in inclusions from magmatic-hydrothermal environments are mostly reported as NaCl (halite), KCl (sylvite) and several other chloride crystals.
Correct identification of the chloride daughter minerals in brine inclusions enables to constrain the composition of ore-forming paleofluids and can help to understand the ways of transport and precipitation of metals from hydrothermal fluids. However, only a limited number of analytical tools can be applied for their identification due to the typically small size of the daughter minerals (usually a few microns in diameter) and their exceptionally high hygroscopicity on opening of the host inclusions. The prime analytical technique is here the Raman spectroscopy that provides a quick, non-destructive and easy available identification method for their identification by comparison with published Raman spectra of chlorides (see recent reviews of Frezzotti et al., 2012 and Hurai et al., 2015). Furthermore, reference spectra of several other synthetic chlorides have been reported just recently: CaCl₂ (Uriarte et al., 2015), K₃NaMnCl₆ (Kurosawa et al., 2016) and KFeCl₃ (Koděra et al., 2017). However, there is still a lack of published Raman spectra of some less common minerals hosted in fluid inclusions or the published spectra of synthetic minerals are different from those found in fluid inclusions for some reasons.

The goal of this work is to provide Raman spectrum of synthetic KCaCl₃ and to understand the differences of Raman spectra collected from synthetic and natural CaCl₂ samples. Raman spectra of all these chloride solids have been calculated using *ab initio* density-functional theory (DFT) and compared with those of synthetic solids and those solids in natural inclusions. Naturally occurring anhydrous chloride minerals, found in halite and apatite from the Siberian Large Igneous Province were used for this purpose. The results of this study can be applied for a clear identification of these minerals in highly saline fluid inclusions by Raman spectroscopy.

## 2. GEOLOGICAL BACKGROUND

The samples with studied inclusions were taken from endogenic deposits of the Siberian Platform (Fig. 1). The Siberian Platform has been subjected to intensive magmatic activity in the Permian to Early Triassic time. The Siberian Traps represent one of the most voluminous flood basalt provinces on the Earth (Burgess & Bowring, 2015). The basement of the Siberian Traps is heterogeneous and consists of metamorphosed Archean and Early Middle Proterozoic formations (Mazurov & Bondarenko, 1997). The sedimentary cover comprises Riphean and Vendian carbonate terrigenous deposits, Cambrian saliferous carbonates, Middle Palaeozoic terrigenous carbonates, Upper Palaeozoic coal-bearing rocks and Lower Mesozoic volcaniclastic sediments (Kontorovich et al., 1997).
<figure><img src="image_2.png" /><figcaption>Fig. 1. Sample locations shown on the schematic geological map of the Siberian Large Igneous Province, represented by products of Permian to Early Triassic volcanism, emplaced on the Tunguska basin sediments (Archean to Upper Paleozoic), including the extent of Cambrian saliferous carbonates. Modified from Polozov et al. (2016).</figcaption></figure>

Two main features of geology of the Siberian platform are relevant to this study. One is the widespread occurrence of a thick halite-bearing succession among the Lower Cambrian carbonates. The salt thickness is particularly important in the central and southern platform area where it reaches 350 m. The individual salt beds are 10 to 50 m thick, and are often intercalated with dolomites. The second important feature is the ubiquitous presence of dykes, sills and complex volcanic-tectonic edifices. The lateral extent of individual sills reaches up to several tens to hundreds of kilometers. The thickness of sills is highly variable from a few centimeters up to three hundred meters. The maximum total thickness of intrusive bodies within a
sedimentary sequence, as determined in the northwestern part of the Siberian platform, reaches 107 1300 m. The emplacement of the high-temperature gas-saturated magma took place over a rather 108 short period during the Permian and Early Triassic. The sills have caused significant alteration of 109 the sedimentary rocks. The volcanic- tectonic edifices cut through the sedimentary cover from 110 the Vendian to the Lower Triassic and are rooted in the crystalline basement (Mazurov and 111 Bondarenko, 1997). The Siberian Trap event is associated with mineral deposits of various types, 112 including apatite-magnetite mineralization. 113

The huge area of the Cambrian evaporite deposits and intense magmatic activity give a 114 unique opportunity to study salt-magma interaction associated with different styles of magmatic 115 intrusions: 116

I- metamorphosed salts in the vicinity of trap intrusions (Kochumdek); 117

II- halite-magnetite rocks from volcanogenic edifices (Korshunovsk Fe-ore deposit); 118

III- chloride segregations in kimberlites (Udachnaya-East kimberlite pipe). 119

Samples of salts from both I and II environments are external to the magma body and 120 have clearly an evaporite origin (Grishina et al., 1992; Mazurov et al., 2007). The nature of 121 chloride segregations in kimberlites is intensively debated, while a co-magmatic origin of 122 chlorides is mostly suggested (Kamenetsky et al., 2014; Kitayama et al., 2017; D'Eyrames et al., 123 2017), the evaporitic source of chlorides (i.e. xenoliths) is also proposed (Grishina et al., 2014a, 124 2014b; Kopylova et al., 2016). 125

3. SAMPLES 126

Most studied inclusions are hosted by metamorphosed halite from different endogenic 127 environments of the Siberian Igneous Province. Metamorphosed salts in the vicinity of trap 128 intrusions were studied from a deep borehole in Kochumdek, located close to the Kochumdek 129 River, the right tributary of the Podkamennaya Tunguska River in East Siberia. The 130 Kochumdek sample was taken from a depth of 2900 m, 7 m above a 300 m thickness dolerite sill 131 (Fig.2). 132
<figure><img src="image_3.png" /><figcaption>Fig. 2. Images from the rock salt of the Kochumdek borehole: A - core sample from the Kochumdek borehole; B- CaCl₂ inclusion in halite (transmitted light); C – cleavage plate surface with empty cavity of exposed CaCl₂ inclusion, surrounded by CaCl₂-hydrates (reflected light)</figcaption></figure>

Halite-magnetite rock was studied from core samples from the Korshunovsk Fe-ore deposit (Fig. 3A). Cavities filled by halite, a few to 10 centimeters in diameter, are common throughout the magnetite rock and contain euhedral apatite and forsterite crystals (Fig. 3B-E). Unhydrous chlorides were found in halite from cavities, as well as in spatially associated high temperature minerals – in apatite and forsterite.

<figure><img src="image_4.png" /></figure>

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Fig.3. Images from the studied halite-magnetite rock from the Korshunovsk FeO deposit (A) Borehole sample of 143 with halite filling a cavity; (B) Enlarged surface of the cavity, incrusted by euhedral crystals of apatite (C) and 144 forsterite (D) (C and D are SEM images); (E) apatite crystal mounted in epoxy with a polyphase fluid inclusion. 145

Samples of chloride segregations in unserpentinised kimberlites were collected from 146 stockpiles of the Udachnaya pipe (Fig.4). 147

<figure><img src="image_5.png" /><figcaption>Fig. 4. Chloride segregation in kimberlite from the Udachnaya-East pipe.</figcaption></figure>

4. METHODS

From the samples described above, cleavage plates of halite and doubly polished thick 151 sections of apatite crystals (150 to 350 µm thick) were prepared. Fluid inclusion petrography 152 including chronological sequence of fluid inclusions was determined by optical microscopy on 153 an Olympus BX51 microscope combined with an Olympus Color View III camera connected to 154 a PC. The inclusions in apatite and forsterite were exposed to the surface in 155 a water-free environment using oil-based diamond pastes to avoid the 156 loss of water-soluble minerals. After polishing, oil was removed by Pe- 157 troleum Benzene. 158

The microthermometric study of CO₂ inclusions was performed on a Linkam stage 159 (model THMS600). The stage was calibrated against the melting points of pure CO₂ inclusions 160 (−56.6°C) and pure water (0°C). Precision of measurements is estimated to ± 0.1°C. The 161 thermometry of inclusions in forsterite and apatite was carried out on a high-temperature heating 162 stage T-1500 (Osorgin & Tomilenko, 1990). This stage was calibrated against the melting points 163
of synthetic standards : K₂Cr₂O₇ (398°C), CsCl (645°C), NaCl (800°C), Au₀ (1063°C), and Mn₀
(1240°C). Precision of measurements is estimated to ± 5°C.

The composition of inclusions was determined by micro-Raman spectrometry and
scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS)
on an Oxford Instruments INCA Energy 350 microanalyzer with a liquid nitrogen-free Large
area EDS X-Max-80 Silicon Drift Detector installed on a JEOL JSM-6510LV scanning electron
microscope at the Analytical Center for multi-elemental and isotope research SB RAS in
Novosibirsk. EDS spectra were collected at an acquisition time of 60 s, an accelerating voltage
of 15 kV, a beam current of 1 nA, and a spot diameter of ~1 µm. The EDS spectra were
optimised for quantification using the standard XPP procedure included in the INCA Energy 350
software.

The Raman spectra of natural samples were recorded in Novosibirsk on a Horiba Jobin
Yvon LabRam HR800 spectrometer coupled to a 1024 pixel LN/CCD detector. Using as
excitation source the double harmonic of Nd:YAG solid state laser with a narrow band of
nominal wavelength 532 nm and a beam power 30 mW (up to 5 mW on samples; Goryainov et
al., 2014). Raman spectra were collected in back-scattering geometry, using an Olympus BX41
microscope. The spectral resolution of the recorded Stokes side of the Raman spectra was set to
2 cm⁻¹ at Raman shift of ~300 cm⁻¹. This resolution was achieved by using one grating with
1800 grooves/mm and equal 100 µm slit and confocal pin hole. The microscope was equipped
with an Olympus 50x objective lens of WD = 0.37 mm and 0.75 numerical aperture, the focal
spot diameter is ~2 µm. The lines from a Ne lamp were used to calibrate the spectrometer. An
Edge filter eliminates the Rayleigh scattering which suppressed low-frequency Raman spectrum
below 60 cm⁻¹ and attenuated the range of 60-100 cm⁻¹. Residual laser beam permeated
additional calibration and correction of each recorded spectrum. The spectra were recorded in the
-10 to 3800 cm⁻¹ range. The accuracy and precision in the wavenumber Raman shift is ±1 cm⁻¹.
PeakFit software package was used for deconvolution of Raman spectra into Voigt amplitude
contours (Canberra Technical Publications).

For the preparation of synthetic KCaCl₃ sample, the following chemicals were used: KCl
(Sigma-Aldrich, 99.5%), CaCl₂ (CaCl₂, Sigma-Aldrich, 99.9%, dried 3 hours at 250°C), all of
them of reagent quality. Sample preparation consisted of mixture containing 50 mol% KCl and
50 mol% CaCl₂ (molar ratio KCl:CaCl₂ = 1:1). Sample was weighted in a glove box under inert
atmosphere (Ar, Messer, 99.999% purity), homogenized, then introduced in a platinum crucible
and transferred into a preheated furnace at 80°C under dried argon atmosphere. The experiment
197 was done in tightly closed vertical resistance furnace with water cooling. Thereafter, the sample
198 was heated to 760°C at rate of 5 °C/min. The mixture was kept at this temperature during 1 hour
199 and then cooled to room temperature spontaneously. At the end, the sample was homogenized
200 and analyzed by XRD and Raman methods. The temperature control and the data processing
201 were performed using a computerized measuring device, developed at the Institute of Inorganic
202 Chemistry SAS, Bratislava (Multi-component model for thermal analysis data collections -
203 National Instruments™, where the data collections run on-line under Labview™ software). The
204 temperature of the sample was controlled by a Pt-PtRh10 thermocouple, calibrated on the
205 melting points of pure NaCl and NaF. The accuracy of the temperature difference measurement
206 between the temperatures of primary crystallizations of the given mixtures was ± 1°C.

207 The X-ray powder patterns of synthetic KCaCl₃ were collected at the Institute of
208 Inorganic Chemistry, Slovak Academy of Sciences on a PanAnalytical diffractometer equipped
209 with a curved Ge (111) monochromator placed in the primary beam and a linear PSD. In order to
210 achieve a better resolution, Cu Kα radiation was used. The XRD patterns were taken in the 2θ
211 range of 7-90° at room temperature.

212 Micro-Raman analysis of synthetic KCaCl₃ was performed using a DXR SmartRaman
213 spectrometer associated with a DXR Raman microscope (Thermo Scientific). Raman spectra
214 were obtained by rotating the powder sample, immersed in a sealed glass capillary. Spectra were
215 excited at room temperature using the 532 nm line of a Nd:YAG laser, with power emission
216 conditions of 5 mW on the sample surface. Objective lense of 100× with a pinhole or slit
217 aperture of 50 µm was used. Each spectrum was collected with exposure time 5 s and 60
218 accumulations, in order to eliminate accidental contamination by cosmic radiation. Peak position
219 was calibrated using a 520 cm⁻¹ band of Si-wafer and using a neon glow lamp.

220 Calculation details for Raman spectra of CaCl₂

221 Structural optimization, energy and Raman calculation were carried out by the CASTEP
222 software packet (Clark et al., 2005) basing *ab initio* density-functional theory (DFT). Initial
223 structures of CaCl₂ with the space group *Pnnm* (58) (Liu et al., 2007) and *Pbcn* (60)
224 (Tomaszewski, 1992) were fully optimized using the local density approximation (LDA)
225 provided parameterization of Perdew and Zunger (1981) of the numerical results of Ceperley and
226 Alder, 1980. Calculations were performed using Norm Conserving pseudopotentials with
227 3s3p3d4s electrons used as valence for Ca atom and 3s3p3d electrons used as valence for Cl
228 atom. The self-consistent field (SCF) procedure was used with a convergence threshold of 2.0
229 10⁻⁸ eV/atom. Geometry optimizations were performed with a convergence threshold of 0.005
230 eV/Å on the max force, 0.1 GPa on the max stress, and 0.002 Å on the maximum displacement.
231 Energy cutoff was set to be 1000 eV, and the Brillouin zone was sampled by 4 × 4 × 6 k-points
232 for CaCl₂ with space group *Pnnm* and 4 × 4 × 4 points for the CaCl₂ with space group *Pbcn*
233 using the Monkhorst-Pack scheme (Monkhorst and Pack, 1976). The phonon spectra at Γ point
234 and Raman tensors were calculated within density functional perturbation theory and finite
displacement method (Porezag and Pederson, 1996 and Refson et al., 2006), based on the crystal
235 system type. Raman spectra were simulated by a Lorentzian distribution with fixed HWHM
236 equal to 4 cm⁻¹.
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**Calculation details for Raman spectra of KCaCl<sub>3</sub>**

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All the structural optimization, energy and Raman calculation were carried out by the
CASTEP program [1] using the density-functional theory (DFT). Initial orthorhombic structure
of KCaCl₃ with the space group *Pmna* (62) (Seifert et al., 1985) was fully optimized using the
local density approximation (LDA) and gradient corrected (GGA) exchange-correlation
functionals PBE and PBESol. The coordinates of atoms were presented without estimated
standard deviations (esd) (Seifert et al., 1985), so the bond length precision could not be obtained
and quality of Rietveld refinement is unclear.
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5. RESULTS

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5.1. Description of inclusions

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5.1.1. Inclusions in halite

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Halite from reaction zones between intrusive magma and salt rocks is characterized by
abundant solid chloride and brine inclusions, spatially associated with dense CO₂ inclusions
(Fig.5). CO₂-rich phase occurs as intergrowth with chlorides and in isolated monophase
inclusions. KCl and KCaCl₃ mineral inclusions are ubiquitous in the environments of the three
types of magmatic intrusions: at the vicinity of trap intrusions, in halite cavities of magnetite
near basaltic diatreme and in halite segregations in kimberlites. Anhydrous CaCl₂ solid
inclusions were found only in two localities: at Kochumdek in contact with trap intrusion and in
halite cavities of magnetite in Korshunovsk iron ore deposit.
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Kochumdek deposit contain rare samples preserved contact metamorphic halite while
generally metamorphic halite was removed by dissolution during intensive late hydrothermal
activity (Warren, 2016). Abundant CaCl₂ solid inclusions were found often in intergrowth with
KCaCl₃ solids. They are spatially associated with liquid CO₂ inclusions and mineral inclusions
like periclase, diopside, amphibole, muscovite, quartz, sulphur, chalcopyrite, pyrite and
262 pyrrhotite. Homogenisation temperatures of CO₂ inclusions to the liquid phase vary from -9 to -
263 15 °C in halite from Kochumdek (Fig.1 SM). No liquid water was observed visually or by
264 Raman spectroscopy using long acquisition times (30-60 s) and 10 accumulations in this
265 inclusion assemblage.

266 All the solid inclusions presented in this work are anhydrous chloride inclusions as shown
267 by the absence of OH-streching band in their Raman spectrum. They have rounded, cubic,
268 euhedral or irregular shapes (Fig.5). The size of the inclusions varies from several to 200 µm,
269 sometimes reaching 500-600 µm. Intergrowths between different individual chloride minerals
270 are common (Fig.5-A, D, E, F).

271 Brine inclusions, containing KCaCl₃ as daughter minerals were found in hydrothermally
272 recrystallised halite in the environments of all types of intrusion (Fig. 5-I) and in apatite from
273 Korshunovsk Fe ore deposit.

<figure><img src="image_6.png" /></figure>

275 Fig. 5. Photomicrographs of representative anhydrous chloride minerals and coexisting CO₂ inclusions, in halite
276 from different environments: contact with a trap intrusion (A -liquid CO₂ inclusion and B,C-solid CaCl₂ inclusion,
277 coexisting in halite from Kochumdek well. Integrowth of different chlorides from the Korshunovsk Fe-ore deposit
278 (D, E, F). Integrowth of chlorides and CO₂ inclusions from chloride xenoliths in Udachnaya-East pipe kimberlites
279 (G, H,) and brine inclusion with KCaCl3 daughter mineral (I). All photomicrographs are in crossed nicoles. Scale
280 bars are 50 µm. Q-quartz
281 5.1.2. Inclusions in apatite and forsterite

282 Apatite and forsterite from the Korshunovsk FeO deposit contain polycrystalline inclusions
283 that have no liquid water at room temperature. According to combined SEM-EDS and Raman
284 analyses their major components are chloride daughter minerals and an unknown Fe-Mg-OH-
285 bearing silicate. Forsterite from Korshunovsk is considered to be a reaction product between the
286 basalt magma and salt-carbonate sedimentary deposits (Mazurov et al., 2007). According to EDS
287 analyses it is quite Mg-rich (Fo92-96).

288 NaCl, KCl and KCaCl₃ daughter minerals have been found in apatite hosted inclusions and
289 only NaCl, KCl in forsterite hosted inclusions. Melting of chloride daughter minerals in apatite
290 occured at 400-450 °C and melting of Fe-Mg-OH-bearing daughter minerals occurs at 500-540
291 °C. Volume decrease of vapour bubble occured at 600 °C, and then inclusions decrepitated. Total
292 homogenization was observed in forsterite-hosted inclusions at 720-840°C.

293 5.2. Composition of CaCl₂-bearing anhydrous inclusions

294 After opening, solid chloride inclusions transformed immediately to a liquid due to
295 deliquescent properties typical of chloride minerals. Dissolution of KCaCl₃ in moisture resulted
296 in formation of KCl crystals and CaCl₂ solution. After precipitation generally isotropic crystals
297 form inside the cavity of opened inclusion and mostly anisotropic crystals surround the cavity.
298 The SEM images of products of the incongruent dissolution of KCaCl₃ show octahedral crystals
299 in the cavity and a mixture of crystals surrounding the cavity. The elemental composition
300 determined by EDS reveals the presence of K-Cl in octahedral crystals and Ca–K-Cl in the
301 precipitated leachate (Fig. 6). In the case of CaCl₂ inclusions only Ca-Cl was identified by EDS
302 analyses in the precipitated leachate around empty cavities (Fig.2C).

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>
Fig.6. Backscattered electron images of KCaCl₃ inclusions in halite exposed on air (A, B, C) and representative energy dispersive spectra of the leachate from opened inclusion (D, E), Korshunovsk FeO deposit.

**5.3. Raman characterization of natural inclusions**

KCaCl₃ (chlorocalcite) inclusions are common as daughter minerals in fluid inclusions and as individual mineral inclusions in metamorphosed halite. KCaCl₃ was also found in polycrystalline inclusions in apatite from reaction zone of dolerites and salt deposits. The absence of water in these solids was demonstrated by the total absence of symmetric and antisymmetric O-H stretching vibrations in the 2700-4000 cm⁻¹ spectral range of the Raman spectra (Fig.2A, SM). Only bands below 300 cm⁻¹ have been observed with main peaks at 140, 149 and 195 cm⁻¹ wavenumbers which are remarkably constant in between the different samples and match perfectly with the Raman spectra of synthetic KCaCl₃ (see below, Fig. 7).

<figure><img src="image_12.png" /></figure>

Fig. 7. Comparison of Raman spectra of KCaCl₃ from natural inclusions and synthetic powder: 1 - euhedral crystal inclusion in halite (kimberlite pipe Udachnaya-East); 2-4 - daughter minerals inside brine inclusions in halite (kimberlite pipe Udachnaya-East); 5 - daughter mineral in apatite-hosted polyphase inclusion (Korshunovsk Fe-ore deposit); 6, 7 – synthetic KCaCl₃ powder.
320 **CaCl₂**. Almost similar spectra were found in CaCl₂ inclusions of samples from two different localities. The Raman spectra of natural inclusions confirms the presence of an anhydrous phase, 321 due to the absence of bands in the water stretching region (2700-4000 cm⁻¹) (Fig.2B, SM). 322 Spectra of inclusions from the two different localities display all same major peaks position in 323 the low frequency region: 74, 95, 99, 107, 124, 158, 164, 179, 212, 236, 244, 256 (Fig. 8). 324 Differences in the relative intensity of the Raman peaks can be seen even in between the spectra 325 of samples from the same location These differences in relative intensity are attributed to 326 different orientations of the crystals in the samples and the anisotropy of the Raman scattering 327 tensor of these crystals. Not all the bands were observed in every spectrum, particularly when 328 Raman signal is too weak to allow minor bands to be detected above the noise level. 329
<figure><img src="image_13.png" /><figcaption>Fig. 8. Low region Raman spectra of anhydrous CaCl₂ inclusions in halite from Korhunovsk FeO deposit (1-9) and Kochumdek borehole (10-12). Vertical lines show Ag modes.</figcaption></figure>

As can be seen in Figure 9 the Raman spectra of natural inclusions of CaCl₂ are different from reported reference spectra of CaCl₂ *Pnnm* polymorph (Uriarte et al., 2015). *Ab initio* calculations were performed to understand the discrepancy of Raman spectra collected from synthetic and natural CaCl₂ samples.
<figure><img src="image_14.png" /><figcaption>Fig. 9. Comparison of Raman spectra of synthetic CaCl₂ (Uriarte et al., 2015) and representative Raman spectra of natural inclusion in halite from the Korshunovsk Fe-oredeposit.</figcaption></figure>

**5.4. Ab initio computations**

The Raman spectra of CaCl₂ was calculated for two different polymorphs, with space groups Pnnm and Pbcn. Group theory analysis predicts 6 active Raman modes for the CaCl₂ polymorph with *Pnnm* space group: Γ<sub>raman</sub> = 2A<sub>g</sub> + 2B<sub>1g</sub> + B<sub>2g</sub> + B<sub>3g</sub>. The calculated Raman spectrum for this polymorph consists of 5 peaks and one shoulder (Fig. 10, top). The Pbcn space group polymorph has 18 active Raman modes: Γ<sub>raman</sub>=4A<sub>g</sub> + 5B<sub>1g</sub> + 4B<sub>2g</sub> +5B<sub>3g</sub> (Table 3), but due to overlapping and low intensity modes the Raman spectrum of this polymorph displays only13 peaks (Fig. 10, bottom).

<figure><img src="image_15.png" /><figcaption>Fig. 10. Calculated Raman spectra of CaCl₂ *Pnnm* (top) and *Pbcn* (bottom) phases.</figcaption></figure>

Reported XRD results of synthetic CaCl₂ nucleated inside capillaries show the presence of two dehydrated phases, the main phase is hydrophilite, coexisting with the *Pbcn* CaCl₂ polymorph
(Uriarte et al., 2015). Crystal structures of both polymorphs of CaCl₂ (Pnnm and Pbcn) are plotted in Fig. 11, using the data of *ab initio* calculations. In both structures, Ca cations are 6-coordinated, whereas Cl anions are 3-coordinated.

<figure><img src="image_16.png" /><figcaption>Fig. 11. Structures of two polymorphs of CaCl₂: Pnnm (a) and Pbcn (b). In both structures, Cations (dark green balls) are 6-coordinated, whereas Cl anions (light green balls) are 3-coordinated.</figcaption></figure>

As it noted above, there are 6 Raman-active modes for Pnnm polymorph and 18 Raman-active modes for Pbcn polymorph according to the selection rules for spectra. Thus, two CaCl₂ polymorphs can be easily distinguished with Raman scattering spectroscopy due to different numbers of bands. In addition, the intensities and wavenumbers of similar type bands (Ca-Cl stretching, bending etc.) are generally different.

In table 1 the experimental lattice parameters are compared with the ones obtained using DFT for KCaCl₃. As can be seen results from theoretical calculations are in a good agreement with experimental data. It is well known, that LDA calculations underestimate equilibrium lattice parameters, while use of the GGA PBE leads to larger lattice parameters (LeSar, 2013) and our calculation results is in agreement with that fact. Thus, calculated bond lengths obtained using LDA are shorter than experimental and longer than experimental in the case of GGA PBESol. In the case of KCaCl₃, GGA PBESol approximation predicted lattice constants close to experimental ones. Atomic parameters obtained with PPGA PBESol approximation are presented in table 2.

<table><caption>Table 1. Lattice parameters and cell volume of KCaCl₃ obtained from experiment and DFT</caption><thead><tr><th></th><th>experiment</th><th>LDA</th><th>PBE</th><th>PBESol</th></tr></thead><tbody><tr><td>a, Å</td><td>7.561</td><td>7.3966</td><td>7.6487</td><td>7.5362</td></tr><tr><td>b, Å</td><td>10.48</td><td>10.1071</td><td>10.5436</td><td>10.3498</td></tr><tr><td>c, Å</td><td>7.255</td><td>7.0099</td><td>7.3313</td><td>7.1748</td></tr><tr><td>V, Å</td><td>574.9</td><td>524.0478</td><td>591.2435</td><td>559.6301</td></tr></tbody></table>
<table><caption>Table 2. Fractional atomic coordinates of KCaCl₃ obtained using GGA PBESol approximation.</caption><thead><tr><th></th><th>x</th><th>y</th><th>z</th></tr></thead><tbody><tr><td>K</td><td>0.42927</td><td>0.25000</td><td>0.02403</td></tr><tr><td>Ca</td><td>0.00000</td><td>0.00000</td><td>0.00000</td></tr><tr><td>Cl1</td><td>0.19986</td><td>0.05513</td><td>0.30459</td></tr><tr><td>Cl2</td><td>0.53366</td><td>0.25000</td><td>0.60626</td></tr></tbody></table>

<figure><img src="image_17.png" /><figcaption>Fig.12. Comparison of observed Raman spectra of KCaCl₃ synthetic sample with calculated using GGA PBESol, LDA and GGA PBE approximations.</figcaption></figure>

The Raman spectra calculated by CASTEP code are comparable with the experimental spectra of synthetic sample of KCaCl₃ (Fig. 12). There are no imaginary vibrational modes (negative frequencies) for all used approximations, thus, calculated structures of KCaCl₃ are stable. It is clear that there is a good agreement between experimental spectra and the calculated one using GGA PBESol approximation, thus, calculated lattice parameters and atomic coordinates could be used for description of crystal structure of synthetic KCaCl₃.

### Synthesis of KCaCl₃ solid:

The complex KCaCl₃ is congruent, existing in the simply binary system KCl–CaCl₂ at the molar ratio KCl:CaCl₂ = 1:1 (Fig. 3 SM). The sample has been analyzed by XRD method. The pattern of this sample is showed in Fig.4 SM), confirming that the sample is a single-phase product.

## 6. DISCUSSION

Due to similarities in their structure, the majority of anhydrous chlorides displays similar Raman spectra. Thus, positive identification of an unknown daughter mineral in inclusion must be supported by a good fit of all major peaks in terms of their position. This can be obtained by various approaches, including reference to Raman spectrum of a synthetic compound at ambient and/or low temperature and reference to calculated Raman spectrum based on structural data.
## 6.1. Identification of CaCl₂

CaCl₂ (*Pnnm*) has phase transition sequence which is unique among the AX₂ compounds, in a narrow pressure range transform from CaCl₂ (*Pnnm*) into four different phases α -PbO₂ (*Pbcn*), EuI₂ (*P2₁/c*), SrI₂ (*Pbca*), and PbCl₂-type (*Pnma*) structures (Leger et al., 1998). Naturally occuring CaCl₂ (*Pnnm*) (hydrophilite) was discredited and considered to be either antarcticite (CaCl₂·6H₂O) or sinjarite (CaCl₂·2H₂O) (Burke, 2006).

According to the DFT calculations of Raman spectra, we attribute the strong peaks in the published spectrum (Uriarte et al., 2015) of the synthetic CaCl₂ to vibrations of the *Pnnm* polymorph and weak lines to vibrations from the *Pbcn* polymorph (Fig. 14). As can be seen the calculated vibrational frequencies of CaCl₂ polymorphs agree well with experimental results on synthetic CaCl₂.

<figure><img src="image_18.png" /></figure>

406

Fig. 14. Calculated Raman spectra of two polymorphs (top) of CaCl₂ and measured Raman spectra of synthetic CaCl₂ at -172°C (bottom; Uriarte et al., 2015). In order to obtain a better agreement of the simulated Raman spectra of both CaCl₂ polymorphs with the spectrum of synthetic mixture of polymorphs, the intensity of the simulated spectrum of the Pnnm polymorph was reduced 10 times.

<figure><img src="image_19.png" /></figure>

411

Fig. 15. Comparison of the calculated Raman spectrum of natural CaCl₂ hosted by a fluid inclusion in halite (Korshunovsk Fe-ore deposit) with calculated spectrum of the Pnnm polymorph.
In Table 3 and Figure 15 the Raman spectrum of natural CaCl₂ hosted by an inclusion in halite from the Korshunovsk Fe-ore deposit is compared to the calculated Raman spectrum of the *Pbcn* polymorph. Apparently, the peaks intensity and wavenumbers are similar to the calculated *Pbcn* polymorph. The vertical lines in Fig. 8 correspond to the symmetric *A*<sub>g</sub> modes at 73, 99, 165 and 256 cm<sup>-1</sup> of the calculated *Pbcn* phase. The total symmetric *A*<sub>g</sub> modes often exhibit strong Raman intensity, although several *B*<sub>1g</sub>, *B*<sub>2g</sub> and *B*<sub>3g</sub> modes also show a high intensity (Fig. 8). Note that, all Raman spectra from natural CaCl₂ inclusions from this study display a similar Raman shift for all major peaks in the spectra of Figure 8. As explained above the different band intensities for different samples and positions within one sample are attributed to non-fixed orientation of crystals with respect to the direction of the electric field of the exciting laser beam and the anisotropy of Raman scattering tensor of the *Pbcn* phase.

<table><caption>Table 3. Comparison of frequencies of Raman active phonon modes of calculated, synthetic (Uriarte et al., 2015) and natural CaCl₂ samples.</caption><thead><tr><th colspan="2">Synthetic CaCl<sub>2</sub>,<br>(Uriarte et al.,<br>2015)<br>exp.</th><th colspan="2">Natural CaCl<sub>2</sub><br>(this work),<br>exp.</th><th colspan="2">Pbcn, DFT</th><th colspan="2">Pnnm, DFT</th></tr><tr><th>v, cm<sup>-1</sup></th><th>v, cm<sup>-1</sup></th><th>Irreps.</th><th>v, cm<sup>-1</sup></th><th>Irreps.</th><th>v, cm<sup>-1</sup></th><th>Irreps.</th><th>v, cm<sup>-1</sup></th></tr></thead><tbody><tr><td></td><td></td><td>B<sub>3g</sub></td><td>61</td><td>A<sub>g</sub></td><td>65</td><td></td><td></td></tr><tr><td></td><td></td><td>A<sub>g</sub></td><td>70</td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>B<sub>1g</sub></td><td>88</td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>B<sub>3g</sub></td><td>94</td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>B<sub>2g</sub></td><td>97</td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>A<sub>g</sub></td><td>98</td><td></td><td></td><td></td><td></td></tr><tr><td>107</td><td>108</td><td>B<sub>1g</sub></td><td>105</td><td>B<sub>1g</sub></td><td>114</td><td></td><td></td></tr><tr><td>115</td><td>124</td><td>B<sub>1g</sub></td><td>131</td><td></td><td></td><td></td><td></td></tr><tr><td>125</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>157</td><td>158</td><td></td><td></td><td></td><td></td><td>B<sub>3g</sub></td><td>163</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td>B<sub>2g</sub></td><td>166</td></tr><tr><td>162</td><td>165</td><td>A<sub>g</sub></td><td>170</td><td></td><td></td><td></td><td></td></tr><tr><td></td><td>179</td><td>B<sub>2g</sub></td><td>172</td><td></td><td></td><td></td><td></td></tr><tr><td>182</td><td>212</td><td>B<sub>3g</sub></td><td>197</td><td></td><td></td><td></td><td></td></tr><tr><td>211</td><td></td><td></td><td></td><td>A<sub>g</sub></td><td>218</td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>238</td><td>244</td><td>B<sub>2g</sub></td><td>229</td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>B<sub>1g</sub></td><td>236</td><td></td><td></td><td></td><td></td></tr><tr><td>252</td><td></td><td></td><td></td><td></td><td></td><td>B<sub>1g</sub></td><td>257</td></tr><tr><td>260</td><td>256</td><td>B<sub>3g</sub></td><td>257</td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>A<sub>g</sub></td><td>266</td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>B<sub>2g</sub></td><td>270</td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>B<sub>3g</sub></td><td>271</td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>B<sub>1g</sub></td><td>280</td><td></td><td></td><td></td><td></td></tr></tbody></table>
The conditions of CaCl₂ formation are different for studied synthetic and natural samples. Natural CaCl₂ inclusions in the studied halite samples were most likely formed from a melt. Numerical estimation temperature of halite crystallisation in the vicinity of intrusion is 600-700 °C (Kontorovich et al., 1997). This temperature interval is higher than the eutectic temperature in the system NaCl-KCl-CaCl₂ (Rober et al., 1975) which indicates that the crystallization of CaCl₂ inclusions occurred from an anhydrous ionic salt melt. CaCl₂ crystals grown from the melt are sensitive to mechanical stress and may undergo transformation to an α-PbO₂-type structure, which is metastable at room temperature (Anselment, 1985). Such stresses may result from the polydomain structure of the particles and increases on cooling in the ferroelastic phase with increasing spontaneous strain (Unruh et al., 1992). The phase transition of CaCl₂ from CaCl₂ phase (Pnnm, Z = 2) to α - PbO₂ (Pbcn, Z = 4) polymorphs was investigated by the ab initio norm-conserving pseudopotential density functional method (Liu et al., 2007). The transition between the CaCl₂ and α -PbO₂ structures happens at 2.9 Gpa (Liu et al., 2007). In the studied natural halite samples much lower pressure (0.5 Gpa) is estimated using the density of coexisting CO₂ liquid inclusions. This indicates that Pbcn phase could not crystallize in the PT conditions at which crystals of CaCl₂ and KCaCl₃ were formed from the paleomelt. The stresses in natural inclusions might have increased due to increasing spontaneous strain on cooling from 600°C, leading to ferroelastic phase transition at low ambient and high structural phase transition pressures. The starting material for synthesis was CaCl₂·2H₂O heated till 140°C and dehydrated to CaCl₂ (Uriarte et al., 2015). Formation mechanism of different polymorphs in the synthetic sample is unknown and detailed explanation remains to be studied.

## 6.2 Identification of KCaCl₃

Chlorocalcite is a rare chloride mineral, that was originally found in sublimates from active volcanic fumaroles (Anthony et al., 1997), but it was also recently determined as a minor evaporite mineral at some potash deposits in China and Laos (Li et al., 2015). In fluid inclusions, chlorocalcite was first reported as daughter crystals in fluid inclusions in halite from the Prairie Formation (Lowenstein and Spencer, 1990). Raman spectrum of solid KCl·CaCl₂ inclusion in halite at the vicinity of dolerite intrusions have been reported based on tentative identification according to SEM-EDS and ultra-microchemical analysis (Grishina et al., 1992). In non-evaporate rock environment KCaCl₃ was described from SEM-EDS in high temperature fluid inclusions in olivine gems from Zabardad (Clocchiatti, 1981) and chlorocalcite was documented by Kodėra et al. (2015) from salt melt inclusions hosted in vein quartz in the Biely Vrch porphyry gold deposit; however, their identification was just tentative based on FIB-EDS analyses. In order to provide a tool for unequivocal identification of this mineral in our fluid
inclusions, we have prepared a synthetic analogue of chlorocalcite (KCaCl₃) to determine Raman spectrum of this mineral. Furthermore, the Raman spectrum of KCaCl₃ was also calculated by *Ab initio* computations, using the structural data of (Seifert et al., 1985).

As shown in Figure 7 and Table 2 (SM), the main Raman scattering bands of chlorocalcite in natural inclusions correspond to main bands and intensity of peaks of potassium calcium trichloride from the synthetic analogue as well as those calculated from structural data. The minor differences are probably related to admixtures in the natural samples and to different orientation of analyzed crystals.

## 7. CONCLUSIONS

Raman spectroscopy was used to prove the presence of anhydrous CaCl₂ and KCaCl₃ daughter minerals in natural inclusions hosted by high temperature halite from different endogenic environments of the Siberian Igneous Province.

The presence of chlorocalcite (KCaCl₃) was unambiguously determined by the comparison of the Raman spectra of the daughter mineral and synthetic KCaCl₃. This was further supported by *ab initio* density-functional theory (DFT) simulations which were used to calculate the theoretical structure and Raman spectra of KCaCl₃. Theoretical structure was in a good agreement with previously published data on KCaCl₃ structure and the theoretical Raman spectrum with those of natural and synthetic KCaCl₃ samples.

In case of CaCl₂, the collected Raman spectra from natural inclusions appear to be completely different from those of synthetic samples published in literature. *Ab initio* calculations enabled to solve this discrepancy. CaCl₂ (*Pnnm*) has a phase transition sequence which is unique among the AX₂ compounds. Indeed, in a narrow pressure range can crystalize in five different phases. The published Raman spectrum of synthetic CaCl₂ is mainly formed by the *Pnnm* polymorph, which is the most stable phase at room temperature and atmospheric pressure with small contributions of the *Pbcn* polymorph. Our calculated spectra of both of these polymorphs are in a good agreement with the spectra published in literature. The comparison of Raman spectra of naturally occurring CaCl₂ inclusions in halite with the calculated spectra revealed the presence of the *Pbcn* polymorph only. This polymorph is metastable at room PT conditions and it was probably formed on cooling from magmatic to ambient temperatures.

Anhydrous CaCl₂ (*Pbcn*), found in halite from the Siberian Large Igneous Province was unequivocally identified by Raman spectroscopy. This does not contradict to the discreditation of naturally occurring hydrophilite with another space group (*Pnnm*).
## IMPLICATIONS

Well-established Raman spectra of anhydrous chlorides ($KCaCl_3$ and $CaCl_2$ with space groups $Pnnm$ and $Pbcn$) can be used for identification of daughter minerals in fluid inclusions from hydrothermal-magmatic and metamorphic environments.

## ACKNOWLEDGMENTS

The authors are grateful to Dr. Sharigin V. for providing the sample and photograph of chloride segregation from Udachnaya-East pipe and Dr. Polozov A. for drawing the map.

This work is financially supported by the Russian Foundation for Basic Research (grant no. 15-05-09345) and VEGA grant 1/0560/15.

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Supplementary material

637

Identification of anhydrous CaCl₂ and KCaCl₃ in natural inclusions by Raman spectroscopy

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GRISHINA et al.

640

<figure><img src="image_20.png" /></figure>

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Fig. 1 SM. Histogram of homogenization temperatures (Th) and melting temperatures (Tm) of CO₂ inclusions from the Kochumdek rocksalt sample.

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<figure><img src="image_21.png" /><figcaption>Fig. 2 SM. Typical Raman spectra of chloride mineral inclusions in halite showing the absence of water: KCaCl₃ from the chloride segregation in kimberlite of the Udachnaya-East pipe (A); CaCl₂ inclusion from the Kochumdek borehole (B).</figcaption></figure>

<figure><img src="image_22.png" /><figcaption>Fig. 3 SM. The phase diagram of the simply binary system KCl-CaCl₂ (Robert et al., 1975)</figcaption></figure>
<figure><img src="image_23.png" /><figcaption>Fig. 4 SM. Comparison of XRD analysis of the synthetic KCaCl₃, prepared from the mixture of 1KCl:1CaCl₂ (1), with the XRD pattern of KCaCl₃ (2) published by Swanson et al (1969). The XRD pattern of KCaCl₃ prepared in this study contains all known reflections of KCaCl₃ listed by Swanson et al. (1969). No other reflections are observed.</figcaption></figure>

<table><caption>Table 1SM: The positions and intensity of reflections of prepared KCaCl₃ sample (this work) and published pattern of KCaCl₃ (1969); CuKα₁, λ = 1.54056, temp. = 25°C.</caption><thead><tr><th colspan="4">d-spacing</th><th colspan="4">Intensity</th></tr><tr><th>KCaCl<sub>3</sub><sup>1</sup></th><th></th><th>KCaCl<sub>3</sub><sup>2</sup></th><th></th><th>KCaCl<sub>3</sub><sup>1</sup></th><th></th><th>KCaCl<sub>3</sub><sup>2</sup></th><th></th></tr></thead><tbody><tr><td>5.24</td><td>1.86</td><td>5.23</td><td>1.86</td><td>31</td><td>2</td><td>25</td><td>2</td></tr><tr><td>4.69</td><td>1.85</td><td>4.68</td><td>1.85</td><td>2</td><td>5</td><td>6</td><td>12</td></tr><tr><td>3.79</td><td>1.83</td><td>3.78</td><td>1.83</td><td>4</td><td>1</td><td>9</td><td>6</td></tr><tr><td>3.71</td><td>1.81</td><td>3.70</td><td>1.81</td><td>12</td><td>1</td><td>30</td><td>2</td></tr><tr><td>3.63</td><td>1.78</td><td>3.62</td><td>1.78</td><td>2</td><td>2</td><td>5</td><td>8</td></tr><tr><td>3.36</td><td>1.77</td><td>3.35</td><td>1.77</td><td>3</td><td>2</td><td>7</td><td>10</td></tr><tr><td>3.28</td><td>1.76</td><td>3.27</td><td>1.76</td><td>5</td><td>3</td><td>12</td><td>10</td></tr><tr><td>3.20</td><td>1.74</td><td>3.19</td><td>1.75</td><td>3</td><td>1</td><td>14</td><td>2</td></tr><tr><td>3.15</td><td>1.74</td><td>3.14</td><td>1.74</td><td>10</td><td>1</td><td>35</td><td>2</td></tr><tr><td>3.12</td><td>1.72</td><td>3.12</td><td>1.72</td><td>5</td><td>1</td><td>30</td><td>2</td></tr><tr><td>3.07</td><td>1.67</td><td>3.06</td><td>1.67</td><td>4</td><td>1</td><td>18</td><td>2</td></tr><tr><td>2.98</td><td>1.67</td><td>2.98</td><td>1.67</td><td>2</td><td>1</td><td>12</td><td>2</td></tr><tr><td>2.90</td><td>1.66</td><td>2.90</td><td>1.65</td><td>6</td><td>1</td><td>14</td><td>4</td></tr><tr><td>2.82</td><td>1.65</td><td>2.82</td><td>1.64</td><td>6</td><td>1</td><td>14</td><td>4</td></tr><tr><td>2.77</td><td>1.63</td><td>2.77</td><td>1.62</td><td>2</td><td>1</td><td>8</td><td>2</td></tr><tr><td>2.62</td><td>1.60</td><td>2.61</td><td>1.60</td><td>100</td><td>1</td><td>100</td><td>2</td></tr><tr><td>2.56</td><td>1.57</td><td>2.56</td><td>1.57</td><td>2</td><td>1</td><td>8</td><td>2</td></tr><tr><td>2.54</td><td>1.56</td><td>2.54</td><td>1.56</td><td>2</td><td>1</td><td>10</td><td>2</td></tr><tr><td>2.42</td><td>1.55</td><td>2.41</td><td>1.55</td><td>1</td><td>1</td><td>4</td><td>2</td></tr><tr><td>2.38</td><td>1.53</td><td>2.38</td><td>1.53</td><td>6</td><td>1</td><td>16</td><td>2</td></tr><tr><td>2.34</td><td>1.51</td><td>2.34</td><td>1.51</td><td>3</td><td>1</td><td>14</td><td>4</td></tr><tr><td>2.32</td><td>1.51</td><td>2.32</td><td>1.50</td><td>4</td><td>1</td><td>14</td><td>2</td></tr><tr><td>2.25</td><td>1.48</td><td>2.25</td><td>1.48</td><td>1</td><td>1</td><td>4</td><td>2</td></tr><tr><td>2.17</td><td>1.47</td><td>2.16</td><td>1.47</td><td>2</td><td>1</td><td>8</td><td>2</td></tr></tbody></table>
<table><tr><td>2.15</td><td>1.46</td><td>2.15</td><td>1.46</td><td>5</td><td>1</td><td>14</td><td>2</td></tr><tr><td>2.12</td><td>1.46</td><td>2.12</td><td>1.46</td><td>3</td><td>1</td><td>14</td><td>2</td></tr><tr><td>2.11</td><td>1.44</td><td>2.11</td><td>1.44</td><td>5</td><td>1</td><td>25</td><td>2</td></tr><tr><td>2.04</td><td>1.43</td><td>2.04</td><td>1.43</td><td>0</td><td>1</td><td>6</td><td>2</td></tr><tr><td>2.01</td><td>1.41</td><td>2.01</td><td>1.41</td><td>1</td><td>1</td><td>4</td><td>2</td></tr><tr><td>1.97</td><td>1.40</td><td>1.96</td><td>1.40</td><td>1</td><td>1</td><td>4</td><td>2</td></tr><tr><td>1.93</td><td>1.39</td><td>1.92</td><td>1.39</td><td>1</td><td>1</td><td></td><td>2</td></tr><tr><td>1.89</td><td>1.86</td><td>1.89</td><td>1.86</td><td>1</td><td>2</td><td>6</td><td>2</td></tr></table>

663

664 Table 2SM. Frequencies of Raman active phonon modes of synthetic and natural KCaCl<sub>3</sub>

665 in comparison with calculated obtained using GGA PBESol.

<table><thead><tr><th>Synthetic</th><th>Natural</th><th colspan="2">Pnma, DFT</th></tr><tr><th>v, cm<sup>-1</sup></th><th>v, cm<sup>-1</sup></th><th>Irreps.</th><th>v, cm<sup>-1</sup></th></tr></thead><tbody><tr><td></td><td></td><td>A<sub>g</sub></td><td>52.9</td></tr><tr><td>57</td><td>57</td><td>B<sub>1g</sub></td><td>55.0</td></tr><tr><td></td><td></td><td>B<sub>2g</sub></td><td>61.1</td></tr><tr><td>66</td><td></td><td>B<sub>3g</sub></td><td>66.6</td></tr><tr><td>75</td><td>75</td><td>A<sub>g</sub></td><td>70.4</td></tr><tr><td></td><td></td><td>B<sub>2g</sub></td><td>80.1</td></tr><tr><td></td><td></td><td>B<sub>1g</sub></td><td>81.4</td></tr><tr><td>86</td><td>87</td><td>A<sub>g</sub></td><td>88.9</td></tr><tr><td></td><td></td><td>B<sub>3g</sub></td><td>93.8</td></tr><tr><td>97</td><td>98</td><td>A<sub>g</sub></td><td>101.5</td></tr><tr><td></td><td></td><td>B<sub>2g</sub></td><td>101.7</td></tr><tr><td></td><td></td><td>B<sub>2g</sub></td><td>114.5</td></tr><tr><td>128</td><td>129</td><td>B<sub>1g</sub></td><td>126.7</td></tr><tr><td></td><td></td><td>B<sub>3g</sub></td><td>134.3</td></tr><tr><td></td><td></td><td>A<sub>g</sub></td><td>135.0</td></tr><tr><td></td><td></td><td>B<sub>2g</sub></td><td>136.6</td></tr><tr><td>139</td><td>140</td><td>A<sub>g</sub></td><td>137.5</td></tr><tr><td>147</td><td>149</td><td>B<sub>2g</sub></td><td>148.7</td></tr><tr><td></td><td></td><td>B<sub>1g</sub></td><td>190.6</td></tr><tr><td>192</td><td>194</td><td>A<sub>g</sub></td><td>191.7</td></tr><tr><td></td><td></td><td>B<sub>3g</sub></td><td>192.6</td></tr><tr><td></td><td></td><td>B<sub>1g</sub></td><td>233.0</td></tr><tr><td></td><td></td><td>B<sub>2g</sub></td><td>237.4</td></tr><tr><td></td><td></td><td>B<sub>3g</sub></td><td>245.29</td></tr></tbody></table>

666

667