The Crystal Chemistry and the Compressibility of Silicate-Carbonate Minerals: Spurrite, Galuskinite and Tilleyite

Geoscience Frontiers 6 (2015) 771e777

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Research paper The crystal chemistry and the compressibility of silicate-carbonate minerals: Spurrite, galuskinite and tilleyite

Jing Gao, Xiang Wu*, Shan Qin

Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, School of Earth and Space Sciences, Peking University, Beijing 100871, China article info abstract

Article history: Spurrite Ca5(SiO4)2(CO3), galuskinite Ca7(SiO4)3(CO3) and tilleyite Ca5(Si2O7)(CO3)2 are three representa- Received 21 May 2014 tive minerals formed in high-temperature skarns in the silicate-carbonate system. Their crystal chemistry Received in revised form and compressibility have been investigated using ﬁrst-principles theoretical simulation. These minerals 6 January 2015 are structurally described as the combination of interwoven layers constituted by Ca polyhedra and Si Accepted 21 February 2015 polyhedra, with the [CO ] triangles being “separators” to depolymerize the SieCa aggregations. With the Available online 11 March 2015 3 effect of pressure, the Si polyhedra and the [CO3] groups present rigid behaviors whereas the CaeO bonds undergo considerable compression. Several pressure-induced abnormities in the lattice parameter vari- Keywords: ﬁ Silicate-carbonate minerals ations have been identi ed, revealing the existence of subtle changes in the compression process. ¼ ¼ 3 0 ¼ Crystal chemistry Isothermal equations of state parameters are obtained: K0 71.1(1) GPa, V0 1003.31(4) Å and K0 5.4(1) 3 0 Compressibility for spurrite; K0 ¼ 75.0(1) GPa, V0 ¼ 1360.30(7) Å , K0 ¼ 5.4(1) for galuskinite, and K0 ¼ 69.7(3) GPa, 3 0 First principles V0 ¼ 1168.90(2) Å and K0 ¼ 4.0(1) for tilleyite. These compounds have similar K0 values to calcite CaCO3 but are much more compressible than larnite b-Ca2SiO4. Generally for these minerals, the bulk modulus exhibits a negative correlation with the [CO3] proportion. The structural and compressional properties of silicate-carbonate minerals compared with silicates and carbonates are expected to be a guide for further investigations on Si polyhedra and [CO3] coexistent phases. Ó 2015, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

1. Introduction 2009; Galuskina et al., 2009) and Canada (Rosa and Martin, 2010); and it was also found in the pyrometamorphic rocks of The silicate-carbonate systems are geologically important in Hatrurim Formation in Israel where the combustion of organic theoretical and experimental studies because of their close asso- fossil fuel provided a heat source (Sokol et al., 2008). Tilleyite was ciation with diamond origin (Pal’yanov et al., 2002, 2005; Litvin initially discovered in thermally metamorphosed limestones from a et al., 2005, 2008; Bobrov and Litvin, 2011), carbonatite genesis contact zone in California, USA (Larsen and Dunham, 1933), and (Wyllie and Haas, 1965; Brooker and Kjarsgaard, 2011) and contact later confirmed to abound in the high-temperature skarn in Cornet metamorphism and metasomatism of limestone (Treiman and Hill in Romania (Marincea et al., 2001; Pascal et al., 2001; Grice, Essene, 1983; Sklyarov et al., 2013). High-temperature meta- 2005), where spurrite was occasionally found in association. morphism and metasomatism of limestone results in the formation Galuskinite is a newly discovered mineral found in altered silicate- of a variety of skarn minerals, among which spurrite carbonate xenoliths a few meters in diameter in the Birkhin gabbro Ca5(SiO4)2(CO3), galuskinite Ca7(SiO4)3(CO3) and tilleyite Ca5(Si2O7) massif of Russia. It was believed to be the retrograde product of (CO3)2 are three representative products (Lazic et al., 2011). Spurrite skarn alteration, to replace dellaite and to be subsequently occurs characteristically in skarns formed during the shallow substituted by spurrite (Lazic et al., 2011). intrusion of igneous rock into limestone in USA (Tilley, 1929; All three minerals are relatively rare with sporadic occurrences Joesten, 1976), Mexico (Wright, 1908), Russia (Galuskin et al., being reported worldwide, but their complicated structures are of considerable interest to geologists as the models of [SiO4] and [CO3] coexistent phases. The tilleyite crystal structure was initially described roughly by Nockolds (1947) and Tilley (1947), respec- * Corresponding author. E-mail address: [email protected] (X. Wu). tively, and later was determined by Smith (1953) to be monoclinic Peer-review under responsibility of China University of Geosciences (Beijing). with the space group of P21/a (Z ¼ 4). The result was subsequently http://dx.doi.org/10.1016/j.gsf.2015.02.001 1674-9871/Ó 2015, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC- ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 772 J. Gao et al. / Geoscience Frontiers 6 (2015) 771e777 supplemented by Louisnathan and Smith (1970), who defined the dimensions of [Si2O7] groups and the arrangement of Ca coordination tetrahedra. The detailed structure of spurrite was determined to be monoclinic (P21/a and Z ¼ 4) consisting of isolated [SiO4] tetrahedral and [CO3] equilateral triangles linked together by Ca atoms (Smith et al., 1960). A systematic description of spurrite and tilleyite structures was reinvestigated in the study of Grice (2005), who proposed the layer module concept for the structural interpretation for minerals in silicate-carbonate system. After- wards, Lazic et al. (2011) further developed the layer concept to describe the structure of newly-found galuskinite and determined that the galuskinite crystal structure could be considered as a multiploid built by alternating spurrite and larnite modules. Despite the experimental studies of these mineral occurrences and structures in previous reports, few descriptions can be used to interpret their structural relationship with corresponding silicates and carbonates. Here we report a first-principle investigation focusing on the crystal chemistry and the compressional mechanism of these minerals, as well as their comparabilities with silicates and carbonates.

2. First-principles computation details

First-principles investigation based on the density functional theory (DFT) has proved successful in exploring the structural, electronic, optical and elastic properties of a number of minerals (Wu et al., 2006; Wu and Qin, 2010; Brik, 2011). All first principle calculations realized in the present work were carried out using Vienna ab initio simulation package (VASP) with generalized gradient approximation from Perdew, Burke, and Ernzerhof (GGA- PBE) (Perdew et al., 1992) treating the exchange-correlation functional effects. The Kohn-Sham equations were solved with a plane- wave (PW) basis set in the projector-augmented-wave (PAW) method (Blöchl, 1994). A plane wave cutoff 600 eV was used to optimize all structures and Brillouin-zone integration was sampled with a 1 1 1 mesh of k-points based on Monkhorst-Pack scheme (the 2 2 2 mesh has been tested with similar values of the optimized lattice constants). During the structure optimizations, we obtained the minimum total energy at a constant volume with the convergence criterion (the different energy/unit cell <0.01 eV), where lattice parameters and internal coordinates of the atoms were fully relaxed to their lowest energy configuration with a stopping criterion of 10 3 eV, and all forces on atoms converge to less 10 2 eV/Å. The energy-volume relationship was fitted by the third-order Birch-Murnaghan equation of state (Birch, 1947).

3. Results and discussions

3.1. Compressional behavior

Fig. 1 displays the calculated pressure-volume relationship of these minerals. The smooth solid lines are the fit of the computed data using the third-order Birch-Murnaghan equation of state. The compressibility of the considered hosts is approximate with the Figure 1. Calculated pressure-volume data of (a) spurrite, (b) galuskinite and (c) tilleyite fitted to the third-order Birch-Murnaghan equation of state. least-squares fitting values being K0 ¼ 71.1(1) GPa, V0 ¼ 1003.31(4) 3 0 Å and K0 ¼ 5.4(1) for spurrite, K0 ¼ 75.0(1) GPa, V0 ¼ 1360.30(3) 3 0 Å , K0 ¼ 5.4(1) for galuskinite, and K0 ¼ 69.7(3) GPa, 3 0 V0 ¼ 1168.90(2) Å and K0 ¼ 4.0(1) for tilleyite. As the bulk modulus volumes are generally overestimated by w3% relative to the X-ray characterizes the incompressibility of the structure, the low K0 diffraction results, which is a typical for GGA computations. values indicate that these minerals are all highly compressible The theoretical axis lengths of these compounds agree with phases. The derived lattice constants and equilibrium volumes are monotonic decreasing trends with pressure. The normalized axial listed in Table 1, where the experimental results are also included compression, a/a0, b/b0 and c/c0, are plotted in Fig. 2. For spurrite for comparison. The relative difference between the computed (Fig. 2a), b-axis is always the softer orientation compared to a-axis lattice parameters and the experimental is w1%, reflecting the high and c-axis. The compressional anisotropy is weakly dependent on quality of the performed calculations. The calculated equilibrium pressure overall except for a subtle change in relative J. Gao et al. / Geoscience Frontiers 6 (2015) 771e777 773

Table 1 Calculated lattice constants and equilibrium volumes of spurrite, galuskinite and tilleyite, where the experimental results from previous reports are also listed for comparison.

a (Å) b (Å) c (Å) b () V (Å3) References Spurrite 10.577(3) 6.782(3) 14.306(6) 102.12 1003.3(4) This study 10.49(5) 6.705(5) 14.16(5) 101.32(8) 976.6 Smith et al. (1960) 10.484(1) 6.712(1) 14.156(2) 101.27(1) 977.1(2) Grice (2005) 10.496(15) 6.719(8) 14.182(18) 101.38(4) 980.5 Marincea et al. (2013) Galuskinite 18.970(5) 6.794(2) 10.555(5) 92.55 1359(1) This study 18.7872(5) 6.7244(2) 10.4673(2) 90.788(1) 1332.24(6) Lazic et al. (2011) Tilleyite 15.401(6) 10.375(4) 7.602(2) 105.41 1171(1) This study 15.110(3) 10.241(2) 7.578(1) 105.15(1) 1131.9 Rubenach and Cuff (1985) 15.082(3) 10.236(2) 7.572(1) 105.17(1) 1128.3(3) Grice (2005) 15.101(30) 10.253(12) 7.577(13) 105.10(22) 1132.6 Marincea et al. (2013)

Figure 2. Pressure-dependent variations of lattice parameters in (a) spurrite (b) galuskinite and (c) tilleyite, with the broken lines for guidelines. 774 J. Gao et al. / Geoscience Frontiers 6 (2015) 771e777

c-axis is a little compressible than b-axis; (2) in the intermediate- pressure range, both a-axis and c-axis become comparatively rigid than b-axis; and (3) above higher pressures, a-axis records an obvious stiffness, whereas b-axis and c-axis exhibit analogous compressibility. Because the b variation changes from decrease to increase coincidently at w6 GPa, it is tempting to associate the turning in b variation with that in axial compression curves. The alterations in pressure-induced lattice parameter variations in these silicate-carbonate minerals are suggestive of the existence of subtle changes in compressional processes. However, no anomalies in the volume compression can be identiﬁed; we therefore determined no obvious changes have occurred in the compression mechanism over the entire pressure range. It is noteworthy that the [CO3] triangles in spurrite and galuskinite are approximately isosceles, with two longer CeO bonds of w1.31 Å, and a shorter one of w1.28 Å. The result is inconsistent with the equilateral description of [CO3] groups in spurrite given by Smith et al. (1960). The [SiO4] tetrahedra in both minerals are

Figure 3. Pressure-induced bond compressions in (a) spurrite (b) galuskinite and (c) tilleyite.

compressibility between a-axis and c-axis at w12 GPa. The b angle decreases linearly on compression. Axial compressibility of galuskinite also exhibits a relatively compressible b-direction (Fig. 2b), and c-axis always exhibits a larger amount of compression relative Figure 4. (a) The structure of larnite b-Ca2SiO4 projected along b-axis. Two types of Ca fi to a-axis, but the b evolution initially decreases but turns to in- coordination polyhedron can be identi ed with the yellow-colored for [Ca(1)O7] crease at w25 GPa. The variations of normalized axial compression polyhedra and the turquoise-colored for [Ca(2)O8] polyhedra. The [SiO4] tetrahedra are symbolized in blue-face with white-edges. The larnite structure can be considered as of tilleyite are more complicated, with two abnormities occurring an ordered arrangement of layers intersected by vertical planes. (b) Isolated (10-1) w w at 6 and 20 GPa (Fig. 2c), separating into three pressure ranges: module is composed of [CaO7] decahedra, [CaO8] dodecahedra and [SiO4] tetrahedra in (1) below w6GPa,a-axis is the most compressible orientation, and a ratio of 1:1:1. J. Gao et al. / Geoscience Frontiers 6 (2015) 771e777 775 nearly regular tetrahedra with similar SieO distance of w1.65 Å, structure as the structural model because of their structural ho- and this is compatible with the SieO length in most orthosilicates. mologies. In larnite, there are two Ca sites with two types of co- For [Si2O7] groups in tilleyite, two longer SieO bonds of w1.68 Å ordination polyhedron (Fig. 4a): Ca1 have 7-fold coordination with and other shorter bonds of w1.63 Å could be distinguished. Our O atoms, while Ca2 coordinates with eight O atoms. According to theoretical descriptions on the [CO3] triangles and Si-polyhedrons the layer concept (Grice, 2005), the larnite crystal structure can be in these silicate-carbonate minerals are consistent with the described as a layered arrangement parallel to (10-1). The isolated experimental results from Grice (2005). The compressions of CaeO, layer module (Fig. 4b) is composed of [CaO7] decahedra, [CaO8] SieO and CeO bonds are plotted together for comparison in Fig. 3, dodecahedra and the faced-shared [SiO4] tetrahedra in a ratio of where the linear pressure coefficients (b) are also annotated. It is 1:1:1. clear that the CaeO bonds are much more compressible relative to The spurrite structure also contains two types of Ca polyhedra the stiff SieO and CeO bonds. So the unit-cell contraction of these but five Ca sites (Fig. 5a). Two kinds of layers on (001) can be compounds is mostly accomplished by the compression of Ca sites. distinguished. One is the central layer assembled from eight- coordinate polyhedra of Ca2 and Ca3, edge-shared with [SiO4] 3.2. Crystal chemistry tetrahedra; and the other is the side layer consisting of [Ca(1)O8] distorted cube, alternate decahedra of [Ca(4)O7] and [Ca(5)O7], and Both spurrite and galuskinite are orthosilicates whereas tilleyite [SiO4] tetrahedra (Fig. 5b). Both layer modules have the larnite is a sorosilicate, all of which contain additional [CO3] groups. It is composition, and the total structure is the interwoven of such two logical to first interpret the larnite b-Ca2SiO4 (P21/n,Z¼ 4) crystal

Figure 5. (a) The structure of spurrite projected along b-axis with the same symbols as in Fig. 4. The [CO3] triangles are colored in black. Vertical planes intersect the structure Figure 6. (a) The structure of galuskinite projected along b-axis with the same sym- in layered modules parallel to (10-1), and separate the structure to two types of layers. bols as in Fig. 5. Vertical planes intersect the structure along the layered arrangement

(b) Isolated (001) layer module consists of [Ca(1)O8] dodecahedra, alternate decahedra of (100), and separate the structure to two types of layer modules. (b) Part of the of [Ca(4)O7] and [Ca(5)O7], and [SiO4] tetrahedra in a ratio of 1:1:1. “spurrite module” and (c) the isolated “larnite module”. 776 J. Gao et al. / Geoscience Frontiers 6 (2015) 771e777 types of layers. The [CO3] triangles in the structure can be consid- layers are separated by [CO3] triangles, and the total composition ered as “separators” to depolymerize the SieCa aggregations. can be taken as Ca3(Si2O7)þ2CaCO3. Overall, the spurrite composition could be roughly deemed as In conclusion, these Si polyhedra and [CO3] minerals share some 2Ca2SiO4þCaCO3. structural characteristics: all the structural templates are the The galuskinite structure is layered on (100), and has been combination of interwoven layers constituted by Ca polyhedra and described as a 1:1 polysome built by alternating spurrite and larnite Si polyhedra, where the [CO3] groups play a role of “separators” to modules (Lazic et al., 2011)(Fig. 6a). The “spurrite module” is made depolymerize the Si-Ca aggregations, and each mineral can isolate a of a sheet [Ca(3)O8]-[Ca(6)O8]-[SiO4], plus the sheet of [Ca(4)O7], CaCO3 component. Grice (2005) stated that the [CO3] triangles in alternate decahedra of [Ca(1)O7] and [Ca(7)O7], and [SiO4] tetra- [SiO4]-bearing compounds tend to edge-link Ca polyhedra with hedra (Fig. 6b). These sheets are separated by [CO3] triangles along lower Lewis-acid strength. The preference is attributed to the lower the ac-plane. The layer situated outside the “spurrite module” is Lewis-base strength of [CO3] triangles relative to the [SiO4] tetra- made up of [Ca(5)O7]-[Ca(2)O8]-[SiO4](Fig. 6c), which exhibits hedra. The valence matching principle was later adopted by Lazic strikingly similar to the larnite module, irrespective of the [SiO4] et al. (2011) to explain the polyhedral connections in galuskinite. tetrahedron connecting two edges with Ca polyhedra.

In tilleyite structure, two [SiO4] tetrahedra share a common O 3.3. Comparison of [CO3]-containing silicates with carbonates and atom to form a sorosilicate [Si2O7] group along the c-axis, which is silicates the feature of sorosilicate. However, hardly a common sorosilicate can be selected as a proper model because tilleyite is structurally Our fully relaxed calculations show no obvious discontinuities distinct. As seen in Fig. 7a, the coplanar [CO3] triangles are skewed occur during the structure compression of these minerals, except to c-axis, and the six-fold coordinated Ca1 can be defined besides for subtle abnormities in the evolution of lattice parameters. We [CaO7] polyhedra of Ca2, Ca4, Ca5, and [Ca(3)O8] polyhedra. All Ca explain the abnormalities in terms of the existence of complicated polyhedra constitute a continuous mesh wrapping around the coordination polyhedra in the structures and the complex rotations [Si2O7] and [CO3] groups. Tilleyite consists of two types of layer of polyhedra under pressure. Particularly, the Ca-polyhedra are the module along (100). One is the simple polyhedral sheet of distorted most responsible for the volume compression. As there are no such [CaO6] octahedra, and the other is a group of three interconnected complicated polyhedra in carbonate (calcite) or silicate (larnite), chains composed of [Ca(4)O7]-[Ca(5)O7]-[Ca(4)O7], [Si2O7]-[Si2O7], their axial ratio curves display no observable changes. The axial and [Ca(2)O7]-[Ca(3)O8]-[Ca(2)O7] in a ratio of 1:1:1 (Fig. 7b). Both ratios with pressure in spurrite and galuskinite present anisotropy with b-axis being more compressible than the ac-plane. It can be structurally interpreted through the orientation of the [CO3] units, which are parallel to the ac-plane, and exhibit pressure-resistance to a-axis and c-axis. It corresponds to the anisotropy in axial compressibility of carbonates, whose the coplanar [CO3] groups are parallel to the ab-plane, and thus the c-axis is distinctly more compressible. The pressure coefficients (b)ofCeO, SieO and CaeO bonds are averaged to be w0.5 10 3, w0.8 10 3 and w2.0 10 3, respectively. Comparing with the data of calcite (Brik, 2011), which has the compressibility of 0.82 10 3 ÅGPa 1 for CeO and 5.3 10 3 ÅGPa 1 for CaeO, it is easy to find that both the rigid [CO3] units and the compressible Ca polyhedra in minerals are stiffer than in carbonates. In comparison with larnite, these minerals also present much more compressibility irrespective of the structural similarities. The

Figure 8. The negative correlation between the bulk modulus and the [CO3] wt.%. The Figure 7. (a) The structure of tilleyite projected along b-axis with the same symbols as K0 values of larnite and calcite are referred to the work of Fiquet et al. (1994) and Remy in Figs. 5 and 6. The distorted [CaO6] octahedra are orange-colored. Vertical planes et al. (1997), respectively. Standard deviations on K0 values of silicate-carbonate intersect the structure in layered modules on (100), and separate the structure to two minerals are smaller than data points, while larnite with the error bars correspond types of layers. (b) Isolated (100) module. to a w9% uncertainty. J. Gao et al. / Geoscience Frontiers 6 (2015) 771e777 777 bulk modulus associated with larnite was estimated to be Galuskina, I.O., Lazic, B., Armbruster, T., Galuskin, E.V., Gazeev, V.M., Zadov, A.E., 0 Pertsev, N.N., Jezak,_ L., Wrzalik, R., Gurbanov, A.G., 2009. Kumtyubeite K0 ¼ 166(15) GPa with K0 being fixed at 4 (Remy et al., 1997). But Ca5(SiO4)2F2-a new calcium mineral of the humite group from Northern Cau- the bulk modulus of spurrite, galuskinite, and tilleyite are generally casus, Kabardino-Balkaria, Russia. American Mineralogist 94, 1361e1370. calculated to be w70 GPa. The distinction in structure compress- Grice, J.D., 2005. The structure of spurrite, tilleyite and scawtite, and relationships to other silicate-carbonate minerals. The Canadian Mineralogist 43, 1489e1500. ibility is mainly due to the [CO3] groups. As seen in Fig. 4a, the Joesten, R., 1976. High-temperature contact metamorphism of carbonate rocks in a larnite layers are directly interconnected through [SiO4] tetrahedra shallow crustal environment, Christmas Mountains, Big Bend region, Texas. and [CaO7] polyhedra. In contrast in minerals, the SieCa aggrega- American Mineralogist 61, 776e781. Larsen, E.S., Dunham, K.C., 1933. Tilleyite, a new mineral from the contact zone at tions are separated by [CO3] groups, leading to a relatively looser Crestmore, California. American Mineralogist 18, 469e473. structure. Thus the compressibility in these compounds should be Lazic, B., Armbruster, T., Savelyeva, V.B., Zadov, A.E., Pertsev, N.N., Dzierzanowski,_ P., more than in larnite due to the existence of voids. Nonetheless, the 2011. Galuskinite, Ca7(SiO4)3(CO3), a new skarn mineral from the Birkhin gabbro massif, Eastern Siberia, Russia. Mineralogical Magazine 75 (5), 2631e2648. K0 values of these minerals are close to those measured for calcite ¼ 0 ¼ fi Litvin, Yu A., Kurat, G., Dobosi, G., 2005. Experimental study of diamondite for- with K0 69.5(2.1) GPa and K0 4( xed) (Fiquet et al., 1994). To mation in carbonate-silicate melts: a model approach to natural processes. understand the correlation between the structural compressibility Russian Geology and Geophysics 46 (12), 1304e1317. and the [CO3] proportion, we summarized the K0 values in min- Litvin, Yu A., Litvin, V Yu, Kadik, A.A., 2008. Experimental characterization of dia- erals, larnite and calcite, and drew them out as a function of the mond crystallization in melts of mantle silicate-carbonate-carbon systems at 7.0-8.5 GPa. Geochemistry International 46 (6), 531e553. [CO3] wt.% in Fig. 8. Obviously, the K0 value has a negative corre- Louisnathan, S.J., Smith, J.V., 1970. Crystal structure of tilleyite: Refinement and e lation with the [CO3] wt.%. That is, the existence of the [CO3] units coordination. Zeitschrift für Kristallographie, Bd 132, 288 306. could improve the compressibility of the structure. And conversely, Marincea, S¸ ., Bilal, E., Verkaeren, J., Pascal, M.L., Fonteilles, M., 2001. Superposed parageneses in the spurrite-, tilleyite-, and gehlenite-bearing skarns from the higher Si polyhedra proportion, the more incompressible of the Cornet Hill, Apuseni Mountains, Romania. The Canadian Mineralogist 39, mineral. 1435e1453. Marincea, S¸ ., Dumitras¸ , D.G., Calin, N., Anason, A.M., Fransolet, A.M., Hatert, F., 2013. Spurrite, tilleyite and associated minerals in the exoskarn zone from Cornet Hill 4. Conclusions (Metaliferi Massif, Apuseni Mountains, Romania). The Canadian Mineralogist 51, 1435e1453359-375. The present study provides an intensive investigation on the Nockolds, S.R., 1947. On tilleyite and its associated minerals from Carlingford, Ireland. Mineralogical Magazine 28 (198), 151e158. crystal chemistry and the compressibility of three representative Pal’yanov, Y.N., Sokol, A.G., Borzdov, Y.M., Khokhryakov, A.F., Sobolev, N.V., 2002. silicate-carbonate minerals: spurrite Ca5(SiO4)2(CO3), galuskinite Diamond formation through carbonate-silicate interaction. American Mineral- ogist 87, 1009e1013. Ca7(SiO4)3(CO3) and tilleyite Ca5(Si2O7)(CO3)2 by means of first- Pal’yanov, Y.N., Sokol, A.G., Tomilenko, A.A., Sobolev, N.V., 2005. Conditions of principles simulation. These minerals are structurally layered as diamond formation through carbonate-silicate interaction. European Journal of defined by Ca polyhedra and Si polyhedra, where the [CO3] groups Mineralogy 17, 207e214. act as “separators” to depolymerize the Si-Ca aggregations. Each Pascal, M.L., Fonteilles, M., Verkaeren, J., Piret, R., Marincea, S¸ ., 2001. The melilite- layer in spurrite and galuskinite has the larnite b-Ca SiO module, bearing high-temperature skarns of the Apuseni Mountains, Carpathians, 2 4 Romania. The Canadian Mineralogist 39 (5), 1405e1434. and all compounds have an isolate CaCO3 component. The Perdew, J.P., Chevary, J.A., Vosko, S.H., Jackson, K.A., Pederson, M.R., Singh, D.J., complicated structure plus the complex rotation of polyhedra with Fiolnais, C., 1992. Atoms, molecules, solids, and surfaces: applications of the pressure result in several abnormities in lattice parameters generalized gradient approximation for exchange and correlation. Physical Review, B 46 (11), 6671e6687. compression curves. Fitting to the third-order Birch-Murnaghan Rubenach, M.J., Cuff, C., 1985. The occurrence of coarse-grained massive tilleyite in equation of state, isothermal parameters are obtained as the Redcap Creek magmatic skarn, North Queensland. Mineralogical Magazine 0 49, 71e75. K0 ¼ 71.1(1) GPa, K0 ¼ 5.4(1) for spurrite; K0 ¼ 75.0(1) GPa, 0 ¼ ¼ 0 ¼ Remy, C., Andrault, D., Madon, M., 1997. High-temperature, high-pressure X-ray K0 5.4(1) for galuskinite; and K0 69.7(3) GPa, K0 4.0(1) for investigation of dicalcium silicate. Journal of the American Ceramic Society 80 tilleyite. The low K0 values are compatible with the compressible (4), 851e860. behaviors of these compounds. In comparison with the data of Rosa, D.F., Martin, R.F., 2010. A spurrite-, merwinite- and srebrodolskite-bearing b skarn assemblage, West Clearwater Lake Impact Crater, Northern Quebec. The larnite -Ca2SiO4 and calcite CaCO3, a negative correlation between Canadian Mineralogist 48 (6), 1519e1532. the bulk modulus and the [CO3] content has been determined. Sklyarov, E.V., Fedorovsky, V.S., Kotov, A.B., Lavrenchuk, A.V., Mazukabzov, A.M., Starikova, A.E., 2013. Carbonate and silicate-carbonate injection complexes in collision systems: the West Baikal Region as an example. 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