Biogenic crystals

Some of the differences in solubilities are also related to different disordering of the crystal surface. As shown by Bishop et al. (1987) with Raman investigations, the biogenic phases are characterized by greater positional disorder than synthetic minerals of the same composition. 

Fig. 7.14 Normalized decrease of the magnetization for magnetites of different origin. Whole cells refer to magnetotactic bacteria, extracted to biogenic magnetite extracted form these. The number indicates the size of synthetic magnetite crystals in nm (modified from Moskovitz etal., 1993, with permission).

Biogenic hpidocrodte was first discovered by Lowenstam (1967) in the radula teeth of a chiton. The crystals are lath-shaped and several tenths of xm long with terminal 101 faces (Webb et al., 1989) (see Fig. 4.14a). The lepidocrocite is often associated with magnetite and ferrihydrite suggesting an Fe" precursor (see Chap. 13). 

Biogenic magnetite may persist once the organism that produced it has died and may, therefore, contribute to the natural magnetic remanence of sediments (Stolz et al., 1986). The discovery in a calcareous Martian ( ) meteorite found in Antarctica, of magnetite crystals with properties very similar to these biogenic magnetites, sup-... 

D.A. (1993) Rock magnetic criteria for the detection of biogenic magnetite. Earth Planetary Sci. Letters 120 283-300 Moukassi, M. Gougeon, M. Steinmetz, P. Dupre, B. Gleitzer, C. (1984) Hydrogen reduction of single crystals of wiistite doped with Mg, Mn, Ca, A1 and Si. Met. Trans. 15B 383-390... 

Mans, B.J. et al. (2007) The crystal structure of D7r4, a salivary biogenic amine-binding protein from the malaria mosquito anopheles gambiae. J. Biol. Chem., 282 (50), 36626-36633. 

Because of its mineral composition, the large size of its phosphate crystals and the small amount of pore space, mature tooth enamel is rarely affected by diagenetic contamination (40-42). This has been supported by experimental data that show that enamel reliably retains biogenic strontium isotope signatures (30, 43-48). 

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