Albite and microcline at pressure Images of the crystal structures of albite, NaAlSi₃O₈, and microcline KAlSi₃O₈ as a function of pressure. The grey tetrahedra represent AlO₄ groups while the red tetrahedra represent SiO₄. The green spheres are Na or K. The view is down the b-axis. The pressure range of the movie is 0 - 20 GPa, extrapolated from the observed data. The data for albite was obtained from Downs, R.T., Hazen, R.M. and Finger, L.W. (1994) The high-pressure crystal chemistry of low albite and the origin of the pressure dependency of Al-Si ordering. American Mineralogist, 79, 1042-1052. The data for microcline was obtained from Allan, D.R., and Angel, R.J. (1997) A high-pressure structural study of microcline (KAlSi₃O₈) to 7 GPa. European Journal of Mineralogy, 9, 263-275.