ABSTRACT

Differential thermal analyses were conducted on protodolomite bearing carbonate rocks of the Riukiu limestone in southern Okinawa. The light-colored portion which is composed of protodolomite and calcite shows two endothermic peaks, while the dark-colored portion shows three endothermic peaks at 780∼790°C (medium), 800∼810°C (weak), and 925∼935°C (strong), respectively. These three endothermic peaks indicate the occurrence of ferroan-dolomite, protodolomite and calcite. The occurrence of pyrite was also confirmed by DTA, X-ray and chemical analyses of residues of the dark-colored samples insoluble in dilute hydrochloric acid. It is concluded that the dark-colored portion is composed of calcite, protodolomite, magnesian-calcite, ferroan-dolomite, aragonite and pyrite. The dark color and the amount of K₂Cr₂O₇-consumption of the carbonate rocks are dependent chiefly on the associated pyrite.