摘要
Spurrite Ca5（SiO4）2（CO3）,galuskinite Ca7（SiO4）3（CO3） and tilleyite Ca5（Si2O7）（CO3）2are three representative minerals formed in high-temperature skarns in the silicate-carbonate system.Their crystal chemistry and compressibility have been investigated using first-principles theoretical simulation.These minerals are structurally described as the combination of interwoven layers constituted by Ca polyhedra and Si polyhedra,with the[CO3]triangles being 'separators' to depolymerize the Si-Ca aggregations.With the effect of pressure,the Si polyhedra and the[CO3]groups present rigid behaviors whereas the Ca-0 bonds undergo considerable compression.Several pressure-induced abnormities in the lattice parameter variations have been identified,revealing the existence of subtle changes in the compression process.Isothermal equations of state parameters are obtained:K0= 71.1（1） GPa,V0= 1003.31（4） A3and K0′ = 5.4（1）for spurrite;K0= 75.0（1） GPa.V0= 1360.30（7） A3,K0’ = 5.4（1） for galuskinite,and K0= 69.7（3） GPa,V0= 1168.90（2） A3and K0’ = 4.0（1） for tilleyite.These compounds have similar K0values to calcite CaCO3but are much more compressible than larnite β-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.
Spurrite Ca5（SiO4）2（CO3）,galuskinite Ca7（SiO4）3（CO3） and tilleyite Ca5（Si2O7）（CO3）2are three representative minerals formed in high-temperature skarns in the silicate-carbonate system.Their crystal chemistry and compressibility have been investigated using first-principles theoretical simulation.These minerals are structurally described as the combination of interwoven layers constituted by Ca polyhedra and Si polyhedra,with the[CO3]triangles being 'separators' to depolymerize the Si-Ca aggregations.With the effect of pressure,the Si polyhedra and the[CO3]groups present rigid behaviors whereas the Ca-0 bonds undergo considerable compression.Several pressure-induced abnormities in the lattice parameter variations have been identified,revealing the existence of subtle changes in the compression process.Isothermal equations of state parameters are obtained:K0= 71.1（1） GPa,V0= 1003.31（4） A3and K0′ = 5.4（1）for spurrite;K0= 75.0（1） GPa.V0= 1360.30（7） A3,K0’ = 5.4（1） for galuskinite,and K0= 69.7（3） GPa,V0= 1168.90（2） A3and K0’ = 4.0（1） for tilleyite.These compounds have similar K0values to calcite CaCO3but are much more compressible than larnite β-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.
基金
supported by Natural Science Foundation of China(Grant Nos.U1232204 and 41473056)
