Mg‐bearing quartz solid solutions as structural intermediates between low and high quartz
Alessio Zandonà, B. Rüdinger, Joachim Deubener
Abstract
Abstract Glass powder samples of cordierite composition (doped with 8 mol% TiO 2 ) were heat‐treated to produce a series of increasingly SiO 2 ‐enriched Mg‐bearing quartz solid solutions (Qss). The obtained materials were then analyzed by X‐ray diffraction: Rietveld structural refinements revealed that Mg‐bearing Qss phases possess trigonal symmetry and a compositionally dependent intermediate structural arrangement between those of low and high quartz. High‐temperature diffraction measurements were performed up to 700°C to characterize the thermal expansion behavior of the crystals. At SiO 2 ‐rich compositions, a reversible high‐to‐intermediate inversion of the quartz structure is observed, which shifts with increasing stuffing to lower temperatures than the conventional 573°C for pure quartz. Similarities and differences to the better‐established Li‐bearing Qss are discussed in the text.