ISSN 00167029, Geochemistry International, 2011, Vol. 49, No. 7, pp. 731737. Pleiades Publishing, Ltd., 2011.Original Russian Text L.V. Olysych, M.F. Vigasina, L.V. Melchakova, L.P. Ogorodova, I.V. Pekov, N.V. Chukanov, 2011, published in Geokhimiya, 2011, Vol. 49, No. 7,pp. 772778.

731

INTRODUCTION

This paper continues the thermal and thermochemical studies of cancrinitegroup minerals thatwere begun by the investigation of cancrinite and cancrisilite from the KhibinyLovozero alkaline complexat the Kola Peninsula, Russia [1]. The crystallinestructure of cancrinite (P63 space group) is built up of3D framework consisting of quasilayers of 6memberrings of cornerconnected SiO4 and AlO4 tetrahedra.The structure is penetrated by zeolite channels of twotypes: the broader channels arranged around sixfoldaxis and narrower channels represented by a chain ofcancrinite voids (hexagonally distorted cuboctahedra)along the threefold axis. Cancrinite cavities accommodate cations Na+ and H2O molecules, while wider

channels contain Na+ and Ca2+ cations and Canions [2]. According to our data, most of cancrinitesamples correspond to simplified formula:Na6Ca[Al6Si6O24](CO3) 2H2O (Z = 1). New mineral,kyanoxalite, Na7[Si67Al65O24](24)0.51 5H2O, thehighwater analog of cancrinite of the same spacegroup P63, was recently found in the Lovozero Massif[3].Our IR data imply the existence of a series of cancrinitekyanoxalite solid solutions, with a gradualchange of proportions of carbonbearing frameworkoff anions CO3/24.

The oxalatebearing members of the cancrinitegroup are typomorphic postmagmatic minerals of theLovozero Massif. In particular, kyanoxalite initiallyfound on the Karnasurt and Alluaiv mounts [3] wasrecently discovered by us also on Mt. Flora. This mineral was observed in the albitized pegmatites of itsnorthern slope, which are localized among the rocksof the layered urtitefoyaitelujavrites. The mainminerals of these pegmatites are potassic feldspar,albite, nepheline, sodalite, aegirine, amphiboles of thearfvedsonitemagnesioarfvedsonite series, eudialyte,

O32

and lorenzenite. In addition to proper kyanoxalite,whose IR spectrum contains intense bands of stretch

ing and deformation vibrations of oxalate ion 2

and lacks bands corresponding to C vibrations (fordetails of IR bands of these minerals see [3]), rocksfrom Mt. Flora also contain intermediate phasesbetween this mineral and cancrinite. The members of

this series with variable C /2 ratios are visually indistinguishable and rarely occur in one sample.Here, they substitute Sbearing sodalite with formation of rims up to 5 mm thick, and sometimes complete pseudomorphs up to 1 cm thick. Columnaraggregates of these minerals are formed by elongatedhexagonalprismatic cornflower blue crystals.

In this work, sample from Mt. Flora was studiedwith DTA and IR techniques to determine the thermalevolution of the intermediate member of the cancrinitekyanoxalite series as well as with hightemperature Calvet microcalorimetry to obtain the enthalpy ofits formation.

EXPERIMENTAL

Chemical composition of sample. Data obtained bycomplex methods showed that the mineral fromMt. Flora studied in this work has the following average composition (wt %): Na2O 20.8, K2O 0.6, CaO 0.6,Al2O3 26.5, SiO2 38.6, SO3 0.6, CO2 5.4, H2O 6.7, andsum of 99.8. Concentrations of elements with atomicnumbers higher than 8 were determined using Xrayanalysis on a CamScan scanning electron microscopeequipped with EDS Link INCA Energy (acceleratingvoltage of 15.7 kV, a beam current of 0.5 nA, and scanning area of 16 16 m). The content of water wasdetermined using Alimarin method: sample washeated to 1000C and released water was collected inan absorption tube filled with Mg(ClO4)2. The amount

O42

,

O32

O32 O4

2

Thermal Evolution and Thermochemistry of the CancriniteGroup CarbonateOxalate Mineral

L. V. Olysycha, M. F. Vigasinaa, L. V. Melchakovaa, L. P. Ogorodovaa, I. V. Pekova, and N. V. Chukanovb

aGeological Faculty, Moscow State University, Vorobevy Gory, Moscow, 119899 Russiaemail: logor@geol.msu.ru

bInstitute of Problems of Chemical Physics, Chernogolovka, Moscow Oblast, 142432 RussiaReceived June 2, 2009

Keywords: thermal analysis, calorimetry, IRspectroscopy, oxalatecancrinite, enthalpy of formation.

DOI: 10.1134/S0016702911050089

SHORT COMMUNICATIONS

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OLYSYCH et al.

of CO2 was measured by selective sorption: sampleswere heated to 1000C in oxygen flow and the releasedCO2 was entrapped in an absorption pipe filled withaskarite.

With allowance for variable C /2 ratios inthe mineral, formula was calculated assuming thatwhole sample in general is characterized by the comparable contents of carbonate and oxalate ions, i.e.,corresponds to the average member of the cancrinitekyanoxalite series. This assumption is confirmed byratios of intensities of the corresponding IR bands (seebelow), as well as by amount of H2O (3.6 molecules performula), which falls practically in the middle partbetween ideal values for cancrinite (2.0) and kyanoxalite (5.0). The empirical formula of the studied mineral calculated for (Si + Al) = 12 is as follows:Na6.9K0.1Ca0.1Al5.4Si6.6O24(C2O4)0.4(CO3)0.4(SO4)0.1 3.6 H2O (m.m. = 1015.28 g/mole).

Thermogravimetric studies of ground sample of80 mgweight mineral were carried out using aQ1500D (Hungary) derivatograph from room temperature to1300, with a heating rate of 15C/min.The results of the thermal analysis (Fig. 1) showed thatvolatile loss starts already at 100. Two subsequentuninterrupted stages of weight loss can be identified onthe TG curve: the loss of 10.2% within a range of 100

O32 O4

2

875 and 2.2% within a range of 8751300 (intotal, 12.4%).

IR spectroscopy. IR absorption spectra of startingmineral and its heating products (Fig. 2) wereobtained using a FSM1201 (LOMO, Russia) FourierSpectrometer within the range of 4004000 cm1,with frequencies determined accurate to 2 cm1.Powdered samples (in the proportion 2 mg of sampleper 250 mg of KBr) were pressed into transparent pellets. The spectra were recorded at room temperature inair, with pellets of pure KBr used for comparison.

The IR absorption spectrum of the carbonateoxalate cancrinite from Mt. Flora (Fig. 2a) within arange of 4001300 cm1 is close to those of cancrinite[1] and highSi kyanoxalite [3] (cm1, shshoulder):428, 457, 569, 623, 684, 758sh (deformation vibrations of AlSiO framework); 818 (deformationvibrations of oxalate anion): 997, 1035sh, 1119(stretching vibrations of framework). The band of thedeformation vibrations of carbonate anion with a frequency about 860 cm1 typical of cancrinite spectrumis absent presumably due to its overlapping by intenseband with maximum at 997 cm1. The range of 13001800 cm1 is the most important for identification ofthe carbonbearing members of cancrinite group. Thespectrum of the described sample in this region contains bands typical of carbonate and oxalate groups, aswell as water molecules: 1371 (symmetrical stretching

100 1300C300 500 700 900 1100

TG

DTG

DTA

A B

C D

Fig. 1. Thermal curves of carbonateoxalate cancrinite from Mt. Flora, the Lovozero Massif: (A) 300, (B) 450, (C) 700,(D) 900.

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THERMAL EVOLUTION AND THERMOCHEMISTRY OF THE CANCRINITEGROUP 733

vibrations of oxalate ion): 1395sh, 1472, 1501 (stretching vibrations of carbonate ions allocated in differentcrystallographic sites); 1640 (deformation vibrationsof water molecule); 1711 (antisymmetrical stretchingvibrations of oxalate ion). The region of OH stretching vibrations contains a wide band with three distinctcomponents: 3436, 3536, and 3600 cm1. The profileof this band in the IR spectrum of the mineral fromMt. Flora is similar to that of highSi kyanoxalite [3].

As compared to starting sample, IR spectrum of themineral heated to 300 (Fig. 2b) revealed stretchingvibrations corresponding to the carbonbearing anions(13001800 cm1). The absorption bands correspond

ing to the vibrations of oxalateion became less intenseand were shifted to the lower frequencies (1359 and1691 cm1) as compared to those of the starting mineral (1371 and 1711 cm1), approaching values foundin the IR spectrum of kyanoxalite [3]. This was accompanied by the change of frequencies and growth ofintensity of absorption bands with maximums at 1388and 1436 cm1 corresponding to the stretching vibrations of carbonate ion. The band at 1501 cm1 remainedpractically unchanged. The region of stretching (34003700 cm1) and deformation (1635 cm1) vibrations of2 shows a decrease in band intensity.

400 800 1200 1600 3200 3600 4000

Tra

nsm

itta

nce

, rel

.u.

Wave number, cm1

432 46

257

762

668

7

984

1096

1389

1447 15

05

(e)

400 800 1200 1600 3200 3600 4000

Tra

nsm

itta

nce

, rel

.u.

Wave number, cm1

(f)

400 800 1200 1600 3200 3600 4000

Tra

nsm

itta

nce

, re

l.u.

Wave number, cm1

995 10

36

(c)

431 45

957

562

6 684

758

1116

*135

0+

1389

+14

41 +15

50 >16

38*1

685 34

50

400 800 1200 1600 3200 3600 4000

Tra

nsm

itta

nce

, re

l.u.

Wave number, cm1

(d)

431 45

9

400 800 1200 1600 3200 3600 4000

Tra

nsm

itta

nce

, rel

.u.

Wave number, cm1

(a)

400 800 1200 1600 3200 3600 4000

Tra

nsm

itta

nce

, rel

.u.

Wave number, cm1

(b)

428 4

5756

962

3 684

818

758

997

1035

1119

*137

1+

1395

+14

72+

1501

>16

40*1

711

3436

3536 36

00

434 46

057

462

6 684

759

990 10

3511

16

*135

9+

1388

+14

36+

1501 >

1640

*169

1

3531

3585

573

626 6

8475

8

995

1110

+13

90+

1441

+15

00 >16

38

3490

471

516

579

697

988

1084

Fig. 2. IRspectra of carbonateoxalate cancrinite from Mt. Flora, the Lovozero Massif (a) and products of its heating (bf) totemperatures: (b) 300, (c) 450, (d) 700, (e) 900, (f) 1300 (* stretching vibrations of oxalate ion, + stretchingdeformation vibrations of carbonate ion, ^ deformation vibrations of water molecules).

734

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OLYSYCH et al.

Heating of the sample to 450 leads to the furtherdecrease of water content (Fig. 2c), which is confirmed by the decrease in absorption in the regions ofstretching and deformation vibrations of H2O molecules. The region of stretching vibrations of carbonbearing anions demonstrates the further reorganization of spectrum: a decrease in the intensity of oxalate

ion bands and an increase in the intensity of

bands, especially component at 1441 cm1.

IR spectrum of mineral heated to 700 (Fig. 2d)lacks bands corresponding to the stretching vibrationsof oxalate ion. Simultaneous loss of water and CO2 isconfirmed by the decrease of band intensities in thecorresponding regions of the spectrum.

In the spectrum of the sample heated to 900(Fig. 2e), the absorption bands of 2 are alreadyabsent. The presence of carbonate ion is identified bythe presence of weakened absorption bands in a range of13801510 cm1.The spectrum range of 4001300 cm1

shows the signs of destruction of cancrinite structure.

After heating to the 1300, spectrum of sample(Fig. 2f) corresponds to the nephelinetype phase withresidual elements of cancrinite structure [4].

Thermochemical studies were carried out on a hightemperature (1000) heatflux TianCalvet microcalorimeter (Setaram, France) [5]. The enthalpy offormation was determined by hightemperature meltsolution calorimetry. For these purposes, pelletesmade up of a pressed powdered sample weighing 24 (2 103) mg were dropped from room temperatureinto 2PbO B2O3 melt solvent placed in calorimeter at = 973 K. During calorimetric experiment on dissolution, the mineral was heated from room temperatureto dissolution temperature of ( = 973K) and its dissolution in oxide melt occurred in air and was accompanied by oxidation of oxalate ion according to reac

tion: C2 + 0.5O2 C + CO2. Melt used for

calorimetric dissolution was obtained by fusion of leadand boron oxide in air and contains dissolved oxygen.This is confirmed in experiments on dissolution ofFe2+bearing compounds, Fe2SiO4, FeSiO3 [6]. Thus,the enthalpy H measured in the course of experimenton mineral dissolution, in addition to the heat contentof the mineral [H(973 ) H(298.15 )] andenthalpy of its dissolution dissH(973 ), alsoincludes exothermic effect of the oxidation of oxalateanion oxidH(973 ). Eight measurements of heateffects accompanying mineral dissolution were carried out. Value of H was determined to be 1186.4 17.1 kJ/mol (average value with error calculated with

O32

,

O42 O3

2

probability of 95%). The value of standard enthalpyof mineral formation from elements using reactions

(1)

can be calculated using standard thermochemicalcycle supplemented by reactions related to the oxidation of proper mineral and sodium oxalate. As wasdemonstrated by our experiments, the error in H =[H(973 ) H(298.15 ) + dissH(973 ) +oxidH(973 )] determined for oxalate ion by droptechnique is an order of magnitude higher than valuesof 23% typical of such studies, which presumablyindicates its incomplete oxidation during dissolution.In this relation, the total function H = [H(973 ) H(298.15 ) + oxidH(973 )] of sodium oxalate wasmeasured by dropping 37 (2 103)mg samplefrom room temperature into a calorimeter at =973 K with no solvent present. The average value ofeight measurements is 88.5 1.6 kJ/mol (error wascalculated with a probability of 95%). The device wascalibrated by the same drop technique, by droppingreference samples, platinum and corundum Al2O3,whose thermochemical data were taken from [7].

RESULTS AND CONCLUSIONS

All thermogravimetric and IRspectroscopic datashow that the thermal transformation of oxalatebearing mineral of the cancrinite series in air could be represented as a combination of three main volatileassisted processes: (1) loss of molecular weight at 100875C; (2) oxidation of oxalate ion into carbonate ion:approximate temperature interval from 200250 to

500600; (3) decomposition of C with releaseof gaseous CO2 usually occurs at temperature higherthan 500 and is completed at t < 1300.

The release of H2O and CO2 during heating of thecarbonbearing minerals of cancrinite group is wellstudied [1]. Most interesting fact is the oxidation ofoxalate ion into carbonate ion discovered by us at leastat the first stage, without removal of these anions fromcrystal. This reaction proceeds under air oxygen andinvolves breaking CC bond in the oxalate group with

formation of two carbonate groups: C2 + O2 =

2C A notable shift to the lower frequencies ofbands of CO stretching vibrations in the group

C2 within a temperature range between 20 and300 shows that the oxalate component in the cancrinitetype structure at heating experiences some

2.65Na2O 0.05K2O 2.7Al2O3 6.6SiO2+ + +

+ 0.1CaSO4 0.4Na2CO3 3.6H2O+ +

+ 0.4Na2C2O4 Na6.9K0.1Ca0.1( ) Si6.6Al5.4O24( )=

CO3( )0.4 C2O4( )0.4 SO4( )0.1 3.6H2O,

O32

O42

O32

.

O42

,

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THERMAL EVOLUTION AND THERMOCHEMISTRY OF THE CANCRINITEGROUP 735

transformations (which are not reversible during rapidcooling: IR spectrum was recorded from cooled sam

ple). It is probable that C2 groups are shifted alongaxis in a channel, occupying energetically more favorable position (probability of the occurrence of oxalateions in the kyanoxalite in different structural positionsis shown in [3]), or even change their configuration.The same temperature range marks the onset ofoxalatecarbonate oxidation, which was recorded inIR spectrum by the decrease in the intensity of bandscorresponding to the CO vibrations of the oxalateion and increase in those of carbonate ion. During thisprocess, only one band with frequency 1441 cm1

among all bands corresponding to the vibrations of

C group shows increase in intensity, which indicates that newly formed carbonateions preferentiallymigrated along zeolite channel to accommodate onlyone structural site. The oxidation of oxalate into carbonate was completed yet before 700.

The enthalpy of formation of the studied mineralfrom elements was calculated using calorimetric dataobtained in this work and required thermochemcialvalues for constituents using the following reactions:

(2)

(3)

(4)

(5)

O42

O32

Na6.9K0.1Ca0.1( ) Si6.6Al5.4O24( ) CO3( )0.4 C2O4( )0.4 SO4( )0.1

3.6H2O c., 298 ( ) 0.2O2 g., 973 ( )+

+ melt 973 K( ) 3.45Na2O( 0.05K2O+

+ 2.7Al2O3 6.6SiO2 0.1CaO SO3+ + +

+ 1.2CO2 + 3.6H2O ) sol., 973 ( ),+

2.65Na2O c., 298.15 ( ) melt 973 K( )+

2.65Na2O sol., 973 ( ),

0.43K2O c, 298.15 ( ) melt 973 K( )+

0.43K2O sol., 973 ( ),

2.7Al2O3 c., 298.15 ( ) melt 973 K( )+

2.7Al2O3 sol., 973 ( ),

(6)

(7)

(8)

(9)

(10)

Thus,

(11)

(12)

(13)

(14)

(15)

The values of enthalpies for reactions (2) and (13)were obtained in this work, while those for reactions(38) and (14) were determined earlier in experiments(Table 1), and enthalpy for reaction (9) was calculatedin [11] (Table 1). The value of reaction(15)H of 1.3 0.9 kJ was estimated by us using enthalpies of dissolution of CaO [5], calcite [12], and reference data onheat contents and enthalpies of formation of CaO,CO2, and calcite [7]. With allowance for conditions of

6.6SiO2 c., 298.15 ( ) melt 973 K( )+

6.6SiO2 sol., 973 ( ),

0.1CaSO4 c., 298.15 ( ) melt 973 K( ) +

0.1CaO 0.1SO3+( ) sol., 973 ( ),

0.4Na2CO3 c., 298.15 ( ) melt 973 K( ) +

0.4Na2O 0.4CO2+( ) sol., 973 ( ),

3.6H2O l., 298.15 ( ) melt 973 K( ) +

3.6H2O sol., 973 ( ),

0.4Na2C2O4 g., 298.15 K( ) 0.2O2 g., 973 ( )+

+ melt 973 K( ) 0.4Na2O(

+ 0.8CO2 ) sol., 973 ( ).

reaction(1)H reaction(310)H reaction(2)H=

reaction(10)H reaction(1315)H=

0.4Na2C2O4 c., 298.15 ( ) 0.2O2 g., 973 ( ) +

0.4Na2CO3 c., 973( ) 0.4CO2 g., 973 ( ),+

0.4Na2CO3 c., 973( ) melt 973 K( ) +

0.4Na2O 0.4CO2+( ) sol., 973 ( ),

0.4CO2 g., 973( ) melt 973 K( )+

0.4CO2( ) sol., 973 ( ).

Table 1. Thermochemical data used in calculations of the enthalpy of formation of cancrinitegroup minerals (kJ/mol)

Component [Ho(973 K) Ho(298.15 K) + diss.Ho(973 K)] f (298.15 K)

a

Na2O(c.) 111.8 0.8b 414.8 0.3

K2O(c.) 193.7 1.1b 363.2 2.1

Al2O3(corundum) 107.38 0.59c 1675.7 1.3

SiO2(quartz) 39.43 0.21d 910.7 1.0

Na2CO3(c.) 241.2 0.8b 1129.2 0.3

CaSO4(anhydrite) 131.3 1.6c 1434.5 1.5

H2O(l) 40.9 2.5e 285.8 0.1

Note: a reference data [7], baccording to data [8], c, d, e, calculated using reference data on [Ho(973 K) Ho(298.15 K)] [7] and experimental data on diss.H

o(973 K): c [9], d [5], e [10], f calculated in [11].

Hel

736

GEOCHEMISTRY INTERNATIONAL Vol. 49 No. 7 2011

OLYSYCH et al.

almost infinite dilution, the enthalpy of mixing wastaken to be zero. Using calculated value of enthalpy ofreaction (1) and available reference data on

f (298.15 ) for constituents (Table 1) and sodiumoxalate (1322.3 10 kJ/mol) [13], the standardenthalpy of formation of the studied mineral from elements was calculated using equation (16):

(16)

where i are the stoichiometric coefficients in equation (1). Obtained value (14473 21 kJ/mol) is thefirst determination of the enthalpy of formation ofnatural oxalatebearing mineral of the cancrinitegroup. This value is almost similar to the enthalpy offormation of proper cancrinite(Na6.93Ca0.545K0.01)[(Si6.47Al5.48Fe0.05)24](CO3)1.25 2.30H2O (14490 16 kJ/mol) determined by us[1], which confirms the validity of obtained values.

On the basis of obtained calorimetric data for theintermediate member of the cancrinitekyanoxaliteseries, we calculated the enthalpy of formation of pureoxalate kyanoxalite Na7Si6Al624(C2O4)0.5 5H2O. Forthis purpose, experimental data on mineral studied inthis work were recalculated for molecular mass ofkyanoxalite (m.m. = 1009.41 g/mol). Value

f (298.15 K) calculated using equations (11) and(16) from corrected calorimetric data for pure oxalate(ideal kyanoxalite) is listed in Table 2.

In order to calculate the Gibbs free energies of theformation of the intermediate member of the cancrinitekyanoxalite series and pure oxalate kyanoxalitefrom elements, the unknown value of standardentropy was estimated on the basis of additive schemefrom the average values of entropies for cations andanions in solid matters. Data on entropies of cationsand anions required for calculations were taken from[14], and data on entropy contribution of zeolitewater were taken from [15]. Absent value of entropycontribution for oxalate ion was calculated using dataon S(298.15 K) [14] for lead oxalate. Using thusdetermined values of standard entropy and enthalpiesof formation of intermediate member of the can

Hel

fHel 298.15 K( )mineral reaction(1)H=

+ vifHel 298.15 K( )compi,

Hel

crinitekyanoxalite series and pure oxalate kyanoxalite determined in this work, we calculated

f (298.15 ) for these minerals (Table 2).

ACKNOWLEDGMENTS

We are grateful to A.A. Mukhanova for help indetermination of the chemical composition of themineral.

The work was supported by the Russian Foundation for Basic Research (project nos. 070500130a,080500077a, and 090591330NNIO_a) and agrant of the President of the Russian Federation o(project no. NSH863.2008.5) and Foundation forSupport of Russian Science (I.V.P.)

REFERENCES1. L. P. Ogorodova, L. V. Melchakova, M. F. Vigasina, et al.,

Cancrinite and Cancrisilite in the KhibinaLovozeroAlkaline Complex: Thermochemical and Thermal Data,Geokhimiya 3, 260267 (2009) [Geochem. Int. 47, 260267 (2009)].

2. E. Bonaccorsi and S. Merlino, Modular MicroporousMinerals: CancriniteDavyne and CHS Phases, Rev.Mineral. Geochem. 57, 448449 (2005).

3. N. V. Chukanov, I. V. Pekov, L. V. Olysych, et al., Kyanoxalite, A New Mineral of Cancrinite Group with OxalateOutofFramework Anion from the Lovozero AlkalineMassif (Kola Peninsula), Zap. Mineral. Ova 138 (6),1835.

4. H. H. Moenke, Mineralspektren. B. 2 (Akad. Verlag, Berlin, 1962).

5. I. A. Kiseleva, L. P. Ogorodova, N. D. Topor, andO. G. Chigareva, Thermochemical Study of theCaOMgOSiO2 System, Geokhimiya, No. 12,18111825 (1979).

6. B. J. Wood and O. J. Kleppa, Thermochemistry ofForsteriteFayalite Olivine Solutions, Geochim.Cosmochim. Acta 45, 529534 (1981).

7. R. A. Robie and B. S. Hemingway, ThermodynamicProperties of Minerals and Related Substances at 298.15K and 1 Bar (105 Pascals) Pressure and at Higher Temperatures, U.S. Geol. Surv. Bull, No. 2131, 461 (1995).

8. I. A. Kiseleva, A. Navrotsky, I. A. Belitsky, and B. A. Fursenko, Thermochemical Study of Calcium ZeolitesHeulandite and Stilbite, Am. Mineral 86, 448455(2001).

Gel

Table 2. Thermodynamic data obtained for the intermediate member of cancrinitekyanoxalite and purely oxalate kyanoxalite at T = 298.15 K

Mineral f kJ/mol So, J/K mol f kJ/mol

Carbonateoxalate cancrinite Na6.9K0.1Ca0.1)(Si6.6Al5.4O24)(CO3)0.4 (C2O4)0.4(SO4)0.1 3.6H2O

14473 21* 1023** 13545**

Kyanoaxalite Na7Si6Al6O24(C2O4)0.5 5H2O

14555** 1093** 13489**

Notes: * experimental data, ** calculated data.

Hel , Gel ,

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THERMAL EVOLUTION AND THERMOCHEMISTRY OF THE CANCRINITEGROUP 737

9. L. P. Ogorodova, L. V. Melchakova, I. A. Kiseleva, andI. A. Belitsky, Thermochemical Study of Natural Pollucite, Thermochim. Acta 403, 251256 (2003).

10. A. R. Kotelnikov, Yu. K. Kabalov, T. N. Zezyulya, et al.,Experimental Study of CelestiteBarite Solid Solution,Geokhimiya, No. 12, 12861293 (2000) [Geochem. Int.38, 11811187 (2000)].

11. I. A. Kiseleva and L. P. Ogorodova, About Use of HighTemperature Dissolution Calorimetry for the Determination of the Enthalpy of Formation of HydroxylBearingMinerals by the Example of Talc and Tremolite,Geokhimiya, No. 12, 17451755 (1983).

12. I. A. Kiseleva, A. R. Kotelnikov, K. V. Martynov, et al.,Thermodynamic Properties of StrontianiteWitherite

Solid Solution (Sr,Ba)CO3, Phys. Chem. Minerals 21,392400 (1994).

13. E. G. Lavut and N. V. Chelovskaya, Design and Testingof a Hybrid of Isoperibol and PhaseChange Calorimetersfor Measurements of the Enthalpies of Reactions Requiring Prolonged Heating, J. Chem Thermodyn. 27 (1995).

14. G. B. Naumov, B. N. Ryzhenko, and I. L. Khodakovskii,Reference Book on Thermodynamic Values (for Geologists)(Atomzidat, Moscow, 1971) [in Russian].

15. G. K. Johnson, I. R. Tasker, H. E. Flotow, et al., Thermodynamic Studies of Mordenite, Dehydrated Mordenite, and Gibbsite, Am. Mineral. 77, 8593 (1992).

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