Aragonite formation

A higher temperature of 35 °C was employed for crystallization of calcium carbonate with radical polymerization of sodium acrylate in aqueous solution. When the concentration of sodium acrylate was the same as that of Table 1, the polymorphs of the products obtained when the radical initiators were added to the reaction mixture after incubation for 1 min (run 1) and 3 min (run 2) were amorphous and aragonite, respectively (Table 2). Aragonite formation was also observed when the radical initiators were added to the reaction mixture after incubation for 20 min. These results suggest that... 

Treves, K., Traub, W, Weiner, S., and Addadi, L. (2003) Aragonite formation in the chiton (Mollusca) girdle. Hdv. Chim. Acta, 86,1101-1112. 

The equations governing the age of secondary carbonate deposits stated above assume that all °Th or Pa present in the mineral is formed in situ by radioactive decay of co-precipitated U. Thorium and Pa content at time of formation can often be considered to be negligible in the pure authigenic phase of calcite or aragonite... 

Figure 10. Summary of experimentally determined fractionation factors for Ca isotopes in the formation of foraminifera and coccolith shell carbonate, and for rapid inorganic precipitation of aragonite from an Mg-Ca-Cl solution. Data for the foraminifer G. ornatissima and the coccolith E. huxleyi are from De La Rocha and DePaolo (2000). Data on G. sacculifer are from Nagler et al. (2000). Data for O. universa and aragonite are from Gussone et al. (2003). Two of the forams and the coccolith E. huxleyi have similar fractionation behavior, with an overall fractionation factor of-1 to -1.5%o, and a small temperature dependence of about 0.02 per °C. The foram G. sacculifer appears to have a strongly temperature dependent fractionation factor.

Many mineral species are known to be selectively crystallized by the presence of bacteria. Carbonate minerals, such as calcite, aragonite, hydroxycalcite, and siderite oxide minerals, such as magnetite and todorokite oxalate minerals, such as whewellite and weddellite sulfide minerals, such as pyrite, sphalerite, wurtzite, greigite, and mackinawite and other minerals, such as jarosite, iron-jarosite, and g3q>sum, are known to precipitate in the presence of bacteria. Therefore, investigations have been developed to analyze the formation of banded iron ore by the action of bacteria, and to analyze the ancient environmental conditions of the Earth through the study of fossilized bacteria. 

Bones, teeth, and shells. Living organisms are able to induce the formation of over 60 inorganic compounds.681 Most of these are formed by animals. Two forms of calcium carbonate, calcite and aragonite, predominate.682 These minerals form shells, exoskeleton bones, bones, teeth, and other specialized structures. 

Acidic amino acids seem to play a key role in (1) the fixation of calcium, (2) the nucleation of CaC03 crystals, and (3) the oriented growth of the mineral phase. There appears to be no essential difference between biochemical or geochemical template-induced mineral formation. The only requirement is the presence of a calcium-specific template and an environment suitable for the deposition of calcite or aragonite. 

---