Structure of aluminosilicate glasses and magmas

What is it about?

We construct a model for the composition-dependent structure of aluminosilicates that is based on a simple set of reactions with a single variable parameter that controls the relative importance of the different reaction schemes

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Photo by Jonatan Pie on Unsplash

Photo by Jonatan Pie on Unsplash

Why is it important?

Amorphous aluminosilicates are ubiquitous, finding widespread commercial application and appearing in the geosciences as a major constituent of magmatic fluids. A structure-based explanation of their properties has remained, however, an elusive goal. Here, we address this issue by constructing a model for the composition-dependent structure that is based on a simple set of reactions with a single variable parameter that controls the relative importance of the different reaction schemes. It is found from NMR experiments that the value of this parameter can be predicted from the cation field strength. The model gives an excellent account of the structure of monovalent and divalent cation aluminosilicate glasses. There are some issues, however, for high field-strength trivalent cation aluminosilicate glasses, which are traced to a network-forming role for fivefold coordinated Al atoms and/or oxygen triclusters. The model provides a benchmark for predicting the structure-related properties of aluminosilicate materials, and a starting point for predicting the evolution in the structure of these materials under the extreme conditions encountered in the Earth's interior or in processes such as sharp-contact loading.

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