Ceramics-Silikáty 18, (1) 1 - 9 (1974)

Single crystals of quartz are subject to a high degree of Dauphiné twinning after heating above the transition temperature of the alpha-beta inversion. The X-ray data indicate the presence of 41 % of material in the Dauphiné twin position after repeated heating at 680 °C, while less than 2 % of twinning was found in the starting material. The reversibility of the alpha-beta phase transition holds for the symmetry change from the trigonal low-temperature phase to the hexagonal high-temperature one but the twinning process itself is irreversible.