The ordering behaviour of reedmergnerite,NaBSi3O8

Reedmergnerite (NaBSi₃O₈) has been synthesised hydrothermally from gels containing 10 wt.% excess SiO₂. The degree of B, Si order increases with time at constant temperature and pressure. Complete order is achieved in 250 h at 400° C, P _fluid=1 kbar and in 700 h at 300° C, 1 kbar. Lower pressures and/ or low water contents greatly reduce the rate of ordering. The ordering behaviour of reedmergnerite is insensitive to the composition of the co-existing fluid and this contrasts with the behaviour of albite. It is suggested that ordering takes place by a process of solution and re-precipitation.