Collect. Czech. Chem. Commun. 1986, 51, 516-525

Phase transitions of natural scolecite

Drahoš Rykl, Vojtěch Chalupský and František Pechar

Institute of Geology and Geotechnics, Czechoslovak Academy of Sciences, 182 09 Prague 8


Based on DTA and TGA, the natural zeolite scolecite (Teigarhorn, Iceland) was subjected to decomposition at temperature of 20, 250, 300, 400, 450, 500, 590, 720 and 1 000 °C; the decomposition products were identified by powder X-ray diffraction analysis and infrared spectroscopy. The crystal structure of scolecite remains stable up to 200 °C only; then it begins to transform into a metaphase and at temperatures above 350 °C, into an amorphous phase from which anortite and the high-temperature quartz modification form at 700 - 1 000 °C. Dehydration of scolecite occurs in four steps. A considerable weakening of the O-H stretching vibrations and vanishing of the water bending vibrations occur at 450 °C. The remaining water splits heterolytically and forms structural O-H groups which persist up to 1 00 °C.