Coordination changes occurring in amorphous silica have been studied by analysis of Voronoi and Delaunay tessellations of structures generated by molecular dynamics simulations up to pressures characteristic of the core-mantle boundary. These calculations predict the coexistence of a remarkable variety of silicon coordination environments at pressures above the mantle transition zone. The postoctahedral compression paths identified through the Voronoi and Delaunay constructions and the increase in geometrical entropy that would be expected to be associated with the loss of short-range order may explain the persistence of the low melting slopes determined for many silicates at pressures from 30 to 60 GPa. The simulated glass transforms from fourfold to sixfold coordination asymmetrically, with a significant number passing through a five-coordinated state. Paths of structural change producing sevenfold- and eightfold-coordinated silicon atoms do not necessarily involve coordination changes in unit increments; for example, sixfold coordination states tend to change to eightfold coordination states without passing through the sevenfold state. The large assortment of coordination types precludes a simple, comprehensive model for compression in amorphous silica at high pressure. Anharmonic properties, such as thermal expansivity, do not appear to be affected by changes in geometrical (Voronoi) coordination in the same way that they are dependent on physical coordination defined in terms of average bond lengths. ¿ American Geophysical Union 1991