The effects of sulfur intercalation on the optical properties of artificial 'hackmanite', Na<sub>8</sub>[Al<sub>6</sub>Si<sub>6</sub>O<sub>24</sub>]Cl<sub>1.8</sub>S<sub>0.1</sub>; 'sulfosodalite', Na<sub>8</sub>[Al<sub>6</sub>Si<sub>6</sub>O<sub>24</sub>]S; and natural tugtupite, Na<sub>8</sub>[Be<sub>2</sub>Al<sub>2</sub>Si<sub>8</sub>O<sub>24</sub>](Cl,S)<sub>2-δ</sub>
The minerals ‘hackmanite’ and tugtupite exhibit tenebrescence (reversible photochromism) and photoluminescence; features that are generally attributed to the presence of sulfide species within their structures. But how these optical properties might be affected by intercalating additional amounts of sulfur into their structures was until now unknown. Artificial ‘hackmanite’, Na8[Al6Si6O24]Cl1.8S0.1 and ‘sulfosodalite’, Na8[Al6Si6O24]S were heated with sulfur in evacuated quartz-glass ampoules over the temperature range 450-1050 °C. This work has shown that sulfur intercalation into Na8[Al6Si6O24]Cl1.8S0.1 destroys the tenebrescence and induces a permanently pale blue and, at higher temperature, a pale green coloration. The effect on Na8[Al6Si6O24]S induced similar colorations but of a deeper hue. Annealing tugtupite, Na8[Be2Al2Si8O24](Cl,S)2-x under a sulfur atmosphere over the range 600-700 °C, destroyed the tenebrescence and resulted in a colourless tugtupite; but did not effect the photoluminescence. This suggests that the chemical species responsible for the tenebrescence in tugtupite is unlikely to be the same as that for the luminescence.
Physics and Chemistry of Minerals, 2012, Vol 39, p. 163-168