Effect of high pressure on the refractive index and density of natural aluminosilicate glasses of alkali basalt composition in the SiO2-Al2O3-TiO2-Fe2O3-P2O5-FeO-MnO-CaO-MgO-Na2O-K2O system

The pressure dependence of the refractive index for a natural glass of composition 0.528SiO2 · 0.019TiO2 · 0.102Al2O3 · 0.021Fe2O3 · 0.062FeO · 0.002MnO · 0.081CaO · 0.072MgO · 0.068Na2O · 0.034K2O · 0.011P2O5 at pressures up to 5.0 GPa is determined using a polarizing interference microscope and an apparatus with diamond anvils. The densities and compressibilities of the glass are calculated from the measured refractive indices within the theory of photoelasticity. The results are compared with the data obtained earlier for another glass that has a similar composition but contains a lower concentration of alkali metal oxides. A higher compressibility of the glass under investigation as compared to the compressibility of the glass studied previously is in agreement with the degrees of polymerization that are calculated taking into account the formation of triclusters.