title: Precipitation diagram of calcium carbonate polymorphs: its construction and significance.
abstract: In order to interpret the formation mechanism of calcium carbonate polymorphs, we propose and construct a new 'precipitation diagram', which has two variables: the driving force for nucleation and temperature. The precipitation experiments were carried out by mixing calcium chloride and sodium carbonate aqueous solutions. As a result, a calcite-vaterite co-precipitation zone, a vaterite precipitation zone, a vaterite-aragonite co-precipitation zone and an aragonite precipitation zone can be defined. Theoretical considerations suggest that the steady state nucleation theory can explain well the appearance of these four zones, and the first-order importance of the temperature dependency of surface free energy in the nucleation of aragonite. Furthermore, the addition of an impurity will likely result in the change of these energies, and this precipitation diagram gives a new basis for interpreting the nature of the polymorphs precipitated in both inorganic and biological environments.
authors.affiliation: Department of Earth and Planetary Science, Faculty of Science, Kyoto University, Kitashirakawa-Oiwake, Sakyo-ku, Kyoto 606-8502, Japan. GAAJ-ZENHOKYO Laboratory, Gemmological Association of All Japan, 8F Daiwa-Ueno Building 5-25-11 Ueno Taito-ku, Tokyo 110-0005, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Kawano
authors.forename: Norimasa
authors.initials: N
authors.lastname: Shimobayashi
authors.forename: Akira
authors.initials: A
authors.lastname: Miyake
authors.forename: Masao
authors.initials: M
authors.lastname: Kitamura