Highly tenebrescent hackmanites from natural nepheline

Abstract

Photochromic hackmanites, (Na,K)₈Al₆Si₆O₂₄(Cl,S)₂, were synthesized with a solid state reaction route using natural nepheline, (Na,K)AlSiO₄, as a starting material together with NaCl, KCl and Na₂SO₄. The hackmanite was obtained using NaCl, whereas with KCl the nepheline reacted only partially. In particular, materials synthesized with NaCl showed a deep photochromic color under UV irradiation and good sensitivity to even low solar UV index values. This suggests that the material is well suited for personal solar UV exposure monitoring.