NESQUEHONITE FROM YOSHIKAWA, AICHI PREFECTURE, JAPAN: OCCURRENCE AND THERMAL BEHAVIOUR

Abstract

Nesquehonite, MgCO₃•3H₂O, from Yoshikawa, Aichi Prefecture, the first occurrence in Japan is described. It is found as columnar aggregates covering the encrustment of “yoshikawaite” on the weathered surface of the serpentinite. The X-ray diffraction pattern and the optical properties are identical to those of the previous data.
The nesquehonite is thermally decomposed lastly to periclase through the three intermediate phases, that is, the dehydrate phase (80-200°C), the amorphous phase (210-270°C) and the decarbonate phase (280-480°C). Periclase is produced at 370°C. A few absorption bands characteristic of the decarbonate phase are already found in the infrared spectrum of the amorphous phase.
DTA curve for nesquehonite shows six endotherms with maxima at 132, 176, 216, 420, 507 and 526°C, respectively, and an exotherm at 499°C. The first three endotherms are attributed to the removal of H₂O, and the others to that of CO₂. The exothermic reaction is considered to be coupled with the fifth endothermic one.