The high pressure structure of liquid and glassy anorthite (CaAl(2)Si(2)O(8)) and calcium aluminate (CaAl(2)O(4)) glass was measured by using in situ synchrotron x-ray diffraction in a diamond anvil cell up to 32.4(2) GPa. The results, combined with ab initio molecular dynamics and classical molecular dynamics simulations using a polarizable ion model, reveal a continuous increase in Al coordination by oxygen, with 5-fold coordinated Al dominating at 15 GPa and a preponderance of 6-fold coordinated Al at higher pressures. The development of a peak in the measured total structure factors at 3.1 Å(-1) is interpreted as a signature of changes in topological order. During compression, cation-centred polyhedra develop edge- and face- sharing networks. Above 10 GPa, following the pressure-induced breakdown of the network structure, the anions adopt a structure similar to a random close packing of hard spheres.