Abstract
Aragonite, one of calcium carbonate polymorphs, is crystallographically unstable but commonly found and proved to be stable thermally in calcium carbonate gallstones. In this paper some considerations were made about crystalline stability of the gallstones by thermal analysis compared with samples of coral, shell, calcareous sinter and rock.
Differential thermal analysis (DTA) proved that biochem i c al aragonite like coral and shell transformed to calcite at the lower temperature (310 - 325°C) than those of calcareous sinter (406°C) and rock (507°C). On the other hand, that of gallstones gave no clear peak of transformation.
X-ray diffraction analysis revealed that aragonite of calcareous sinter completed its conversion to calcite at 500°C, while in gallstones only 8 % transformed to calcite at 500°C,56% at 600°C and 69% even at 650°C respectively. Aragonite form of calcium carbonate gallstones proved to be stable thermally.
It is sugg e sted that some organic material in the gallstone affects thermal stability of the aragonite crystal.
