Summary: The course of all crystalline structural changes undergone by the mineral beryl, its melt and glass, has been followed as a function of widely differing but accurately known thermal history. Non-equilibrium ordering processes have been characterized by new techniques in high-temperature microscopy.

The relative influence that beryllium and aluminium ions exert on the phase changes has been established by studies on synthetic melts and glasses representing hypothetical beryls of differing ratios of Be²⁺:Al³⁺ ions.

The dynamic changes between the oxide and orthosilicate structures into which the systems reconstitute include the formation of a metastable hybrid beryllium aluminium silicate, which is viewed as a beryllium-containing mullite. The crystallochemical changes have been interpreted in terms of a structural model of the melts and glasses that is shown to be consistent with the ordering effects predicted from the field strengths of the cations.