Thermal expansion and the high-low transformation in quartz. II. Dilatometric studies

Thermal expansion and contraction of single-crystal quartz, 400 mesh quartz powder, and chert were measured with a highly sensitive dilatometer apparatus. Below 560°C expansion characteristics were identical and in agreement with X-ray diffractometer measurements. Between 571 and 573°C single-crystal quartz expanded with a volume coefficient of 250 × 10^-5 deg^-1 and exhibited 2.5°C hysteresis. Between 571 and 576°C 400 mesh quartz expanded with a volume coefficient of 150 x 10^-5 deg^-1 and exhibited 1°C hysteresis. Chert expanded more gradually between 560 and 650°C, with a maximum volume coefficient of 31 × 10^-5 deg^-1 and exhibited no hysteresis. The results are interpreted in terms of a Dauphiné twinning mechanism and related to observations from the literature, particularly those relating to light-scattering phenomena and strength measurements.