Carbonates carbonate fluorapatite

Of the possible substituting ions, COi ion is by far the most important followed by Na, S04 and Mg. The most common form of natural apatite in sedimentary rocks is francolite, a substituted form of carbonate fluorapatite deposited in marine systems. The substitution of col ior>s into the mineral lattice has a substantial effect on apatite solubility (Jahnke, 1984). More studies are required, however, before the effects of all substituting ions are imderstood and an accurate assessment of the solubility of complex, natural apatites can be made. 

Once fluoride ions react with bone, they are not easily dissolved out or exchanged by other elements. If bone is buried for long periods of time, the relative amount of fluorine in the bone gradually increases as a function of time the "fluoridation" process continues until the maximum amount of fluorine (necessary to convert all the hydroxyapatite to fluorapatite) is reached. The total concentration of fluor in carbonated fluorapatite can reach levels as high as above 3%. There is ample room, therefore, for an increase in the relative amount of fluorine in buried bone. Determining the relative amount of fluorine in buried bone may thus serve as a tool for dating bone. 

Crystallization of the amorphous layer by incorporation of OH-, C032- or F- anions from solution to form a mixed hydroxyl carbonate fluorapatite layer (CHA). 

P. Regnier, A.C. Lasaga, R.A. Berner, O.H. Han, K.W. Zilm, Mechanism of COa substitution in carbonate-fluorapatite Evidence from FTIR spectroscopy, NMR, and quantum mechanical calculations. Am. Mineral. 79 (1994) 809-818. 

H. Sfihi, C. Rey, 1-D and 2-D Double heteronuclear magnetic resonance study of the local structure of type B carbonate fluorapatite, in J. Fraissard, B. Lapina (Eds.), Magnetic Resonance in Colloid and Interface Science, Nato ASI Series II, Vol. 76, Kluwer Academic Publishers, Dordrecht, 2002, pp. 409-422. 

M. Jarlbring, D.E. Sandstrom, O.N. Antzutkin, W. Forsling, Characterzation of active phosphorus surface sites at synthetic carbonate-free fluorapatite using single pulse H, P, and P CP-MAS NMR, Langmuir 22 (2006) 4787 792. 

Apatites with large amounts of fluoride ions the B-type carbonated fluorapatite. 

LEHR and Me CLELLAN (3) demonstrated numerous natural apatites and a correlation between the amount of fluoride ions and that of the carbonate ions. This led them to propose that PO -ions can be replaced by COg - ions associated with F ions. Such a hypothesis could explain the abnormally high amount of fluoride in some FRANC0LITES. However this type of substitution was not proved by the authors. We studied some synthetic apatites where fluoride and carbonate ions were simultaneously introduced. Samples of B-type carbonated fluorapatite (COj - substituting PO -) were obtained as a powder from an aqueous medium rich in fluoride ions and also an aqueous medium poor in fluoride ions. 

However a lack of calcium is observed and the correlation between the amounts of fluoride ions and carbonate ions is not rigorous. This is due to the existence of a second type of substitution as originally proposed by LABARTHE (4-5). According to this author, the substitution of a PO ions by a C0- ion is accompanied by the formation of vacancies in an oxygen site and also in the Ca + and F" sites of the channel which are the closest to the missing oxygen. The B-type carbonated fluorapatite can be described by the formula ... 

The most common and widely distributed phosphate minerals are the apatite group, with the general formula Ca10(PO4)6(X)2. The apatite is designated as fluorapatite, hydroxyapatite, or chlorapatite, when X = F, OH, or Cl, respectively. The most abundant sedimentary apatite is carbonate fluorapatite (ffancolite). Relative to pure fluorapatite, francolite is characterized by the substitution of Na and Mg for Ca and of carbonate and fluoride for phosphate. An empirical formula for francolite... 

Rosseeva EV, Buder J, Simon P, Schwarz U, Frank-Kamenetskaya OV, Kniep R (2008) Synthesis, characterization, and morphogenesis of carbonated fluorapatite-gelatine nanocomposites a complex biomimetic approach toward the mineralization of hard tissues. Chem Mater 20(19) 6003-6013... 

Parker and Siesser, 1972). (b)-(f) Scatter diagrams of selected elements for additional samples from Namibia (Watkins et ah, 1995), East Australia (O Brien et ah, 1990), Peru and Chili (Burnett, 1977), as well as seamount phosphorites from the equatorial Pacific (Hein et al., 1993). The dotted lines in (b) and (c) are the slopes for shale. The dotted lines in (d) and (e) are slopes for carbonate fluorapatites with possible formulas of Nao.5Ca5(P04)2.s (C03)F... 

McArthur J. M. (1978) Systematic variations in the contents of Na, Sr, CO2, and SO4 in marine carbonate-fluorapatite and their relation to weathering. Chem. Geol. 21, 41-52. 

Authigenic Carbonate Fluorapatite (CFA) Modem Phosphorites. Carbonate fluorapatite (CFA), or francolite, is the dominant phosphatic... 

C P)org > Redlield Ratio, accompanied by transformation of Porg to carbonate fluorapatite. 

McArthur J. M. (1980) Post-depositional alteration of the carbonate-fluorapatite phase of Morocccan Phosphates. In Marine Phosphorites. Spec. Publ. 29 (ed. Y. K. Bentor). SEPM, pp. 53-60. 

Minerals of phosphorites are quite simple when compared with those of rock phosphates of magnesium, aluminium and iron. They consist essentially of apatites, whitlockite, monetite and brushite. However, francolite or dahllite (carbonate fluorapatite and carbonate hydroxyapatite) probably comprise more than 99% of the phosphatic constituent of the average phosphorite. 

Reiterating, the phosphatic mineral of such phosphorites is essentially francolite, a carbonate fluorapatite of somewhat variable composition (McConnell, 1971 Rooney and Kerr, 1967). Although not proven to be contained within the apatitic phase through isomorphic substitution, some of the continental phosphorites are of considerable interest because of accumulations of uranium, thorium, yttrium, rare earths, scandium, and vanadium therein. These rarer components are thought to be related to diagenetic processes, in which case they were extracted from sea water during the early formative histories of the phosphorites. 

By far the most abundant phosphate mineral is apatite, which accounts for more than 95% of all P in the Earth s crust. The basic composition of apatite is listed in Table 14-2. Apatite exhibits a hexagonal crystal structure with long open channels parallel to the "c" axis. In its pure form, F, OH, or Cl occupy sites along this axis to form fluorapatite, hydroxyapatite, or chlorapatite, respectively. However, because of the "open" nature of the apatite crystal lattice, many substitutions are possible and "pure" forms of apatite as depicted by the general formula in Table 14-2 are essentially never foxmd. Of the possible substituting ions, carbonate ion is by far the most important followed by Na, SO , and Mg " ". The most common form of natural apatite is francolite, a highly substituted form of carbonate fluorapatite deposited in marine systems. The substitution of CO3 ions into the mineral lattice has a substantial effect on apatite solubility (Jahnke, 1984). More studies are required, however, before the effects of all substituting ions are understood and an accurate assessment of the solubility of complex, natural apatites can be made. 

---