gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1973.039.304.04 Application of Gas Chromatography to Mineral Chemistry: Aluminium-Silicon Ordering in Melilites Lachowski E. E. Glasser F. P. Department of Chemistry, University of Aberdeen, Old Aberdeen, Meston Walk, Aberdeen AB9 2UE, Scotland 12 1973 39 304 412 419 23 2 1973 Copyright © 1973, The Mineralogical Society 1973 Summary

The mole fractions of the silicons present in melilites as monomeric (SiO4) and dimeric (Si2O7) groups depends both upon the composition of the melilite and also upon the degree of Al-Si ordering. It is shown that the absolute numbers of monomeric and dimeric silicons in a 10 mg polycrystalline sample can be determined by a relatively rapid chromatographic method.

A statistical theory is developed to treat the data; this contains a variable κ-parameter that describes the degree of ordering.

Experimental results are presented and interpreted for one natural and five synthetic melilites. The synthetic gehlenite-rich melilites are appreciably, but not completely disordered. The natural melilite is well ordered, but heating at 1050 °C introduces considerable disorder.