Expansion behaviour of commercial vermiculites at 1000 °C

Commercial vermiculites from different places were studied in order to know the cause of their different behaviour after abrupt heating at 1000 °C. Mössbauer spectroscopy provided Fe2+ and Fe3+ contents and allowed identification of both tetrahedral and octahedral iron. The Fe2+ content was higher in type-2 vermiculites (with K+− or > 1 and/or Na+ and/or Ca2+ with or without Mg2+ as the principal interlayer cations) than in type-1 vermiculites (with Mg2+ or Mg2+ and K+ (< 1) as the principal interlayer cations). The higher iron content seemed to facilitate the fixing of potassium ions. This was responsible of the larger expansion after abrupt heating at 1000 °C for 1 min.