Aragonite chemistry

Komicker W.A., Morse J.W., Damascenos R.N. The chemistry of Co2+ interaction with calcite and aragonite surface. Chem Geol 1985 53 229-236. 

A key question is then the relationship between the isotopic composition of the C02(g) in the soil and the CO2 dissolved in the mineral species growing in the soils. The equilibrium carbon isotope fractionations between C02(g) and carbonate minerals (CaC03 (both calcite and aragonite polymorphs), MgC03 (magnesite)) are known experimentally and can be accurately calculated from quantum chemistry (75). Overall, carbon in carbonate minerals is isotopically heavier than carbon in C02(g) by about... 

Fig. 4.5 Crystal structures ofjwo forms of ciilcium carbonate (a) unit cell of calcitc. rhombohedral. space group R3c (b) unit cel of aragonite, orthorhombic, space group Pcmn Circles in decreasing order of size are oxygen, calcium, and carbon. [From Ladd. M. F. C Structure and Bonduiy in Solid State Chemistry Wiley New York, 1979. Reproduced with permission.]...

On a relative basis, i.e. residues per 1000, there is virtually no one species like the other. In contrast, different shell samples from the same species and obtained from the same natural habitat yield identical amino acid patterns. It is of interest that (1) the structure of carbonates (aragonite-calcite-vaterite), (2) the content in trace elements, and (3) the stable isotope distribution are markedly effected by fluctuations in salinity, water temperature, Eh/pH conditions, and some anthropogenic factors. The same environmental parameters determine to a certain degree the chemical composition of the shell organic matrix. This feature suggests a cause-effect relationship between mineralogy and organic chemistry of a shell. In the final analysis, however, it is simply a reflection of the environmentally-controlled dynamics of the cell. 

Polymorph Two or more solid crystalline substances with the same chemistry, but different crystalline structures. Calcite (rhombohedral CaCCE) and aragonite (orthorhombic CaCCE) are polymorphs. 

Millero et al. (1979) summarized data of their own and of other investigators on the carbonate chemistry of the Mediterranean Sea. This sea is interesting, because its waters are supersaturated everywhere with respect to both calcite and aragonite. Both minerals are found in abundance in the sediments. The carbonate system in the Mediterranean Sea may be similar to that found in ancient epicontinental seas. 

Near-surface seawater is typically supersaturated by over six times with respect to calcite, and over four times with respect to aragonite (see Chapter 4). When it flows over shallow areas of the world s oceans, its chemistry can be modified by several different processes. The extent of modification is strongly dependent on the residence time of the water over the shallow areas. Morphologic controls on flow, such as embayments, barrier islands, and reefs, can often lead to significant restriction of the flow of seawater. In areas where these restrictions occur, major changes in the chemistry of the seawater are usually observed. 

Budd D.A. (1988) Aragonite-to-calcite transformation during fresh-water diagenesis of carbonates Insights from pore-water chemistry. Geol. Soc. Amer. Bull. 100, 1260-1270. 

Lorens R.B. and Bender M.L. (1980) The impact of solution chemistry on Mytilus edulis calcite and aragonite. Geochim. Cosmochim. Acta 44, 1265-1278. 

Lowenstam H.A. (1963) Sr/Ca ratio of skeletal aragonites from the recent marine biota at Palau and from fossil gastropods. In Isotopic and Cosmic Chemistry (ed. H. Craig et. al.), pp. 114-132. North Holland Publishing Co., Amsterdam. 

DeKanel, J., and Morse, J.W. (1978) The chemistry of orthophosphate uptake from seawater onto calcite and aragonite. Geochim. Cosmochim. Acta 42, 1335-1340. 

The combustion method is used to obtain rare earth orthoborates such as vaterite type YBO3 and GdBOs and aragonite type LaBOa (Tukia et al., 2005). Soft chemistry methods such as coprecipitation-combustion method, salt assisted combustion method, and emulsion method are employed to prepare the red phosphor (Y,Gd)B03 Eu (Cui et al., 2008). 

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