Biogenic minerals

Figure 1. Histogram of measurements of molar U/Ca ratio in a number of samples of reef-building corals and one giant clam sample (after Edwards 1988). Also indicated is the U/Ca ratio of seawater. This illustrates the point that corals do not fractionate U from Ca by large amounts when they make their skeletons. U/Ca ratios of corals are similar to values from inorganically precipitated marine aragonite. Mollusks along with most other biogenic minerals exclude uranium. Note that the horizontal axis is on a log scale and that the U/Ca ratio of the clam is almost 5 orders of magnitude lower than that of the corals. This difference is the fundamental reason why there are difficulties with uranium-series dating of mollusks.

The fact that the carbonates of foraminifera burried in marine sediments can be used as a "memory storage" for Cd2+ present in the sea when the foraminifera were formed (Delaney and Boyle, 1987) is evidence for the non-reversibility or extremely slow reversibility of biogenic mineral carbonates. 

Table 3. Summary of Fe isotope fractionations during biogenic mineral formation.

Mann, S. Cornell, R.M. Schwertmann, U. (1985) The influence of aluminium on iron oxides XII. High-resolution transmission electron microscopic (HRTEM) study of aluminous goethites. Clay Min. 20 255-262 Mann, S. Perry, C.C. Webb, J. Luke, B. Wil-liams, R.J.P. (1986) Structure, morphology, composition and organization of biogenic minerals in limpet teeth. Proc. R. Soc. Lond. 

Figure 2. Spectra of non-biogenic mineral samples containing OH" (brucite, portlandite, hydrocerussite), liquid 0 (aragonite speleothem) and bound H2O (magnesite, hydrozincite).

Among all the minerals used by organisms, three categories are widely dominant silica, calcium phosphates, and calcium carbonates. Calcium phosphate minerals are usually associated with vertebrates , where they form bone and the dentine and enamel of teeth. However, phosphate minerals are present in some invertebrate shells, such as Brachiopods, whereas vertebrates used calcium carbonate minerals in eggshells and otoliths. Calcium minerals represent about 50% of all biogenic minerals. 

As pointed out before, one must strictly distinguish between distribution or accumulation of chemical elements in biomasses and their functions for the corresponding organism the action need not be where the highest concentrations are but elsewhere, even disregarding inactive top concentrations in biogenic mineral phases such as bones or silica fibres fortifying plant shoots. Distribution and accumulation are related to the stability and variety of metal-biomass complexes (e.g. Wiinschmann et al. 2004) whilst function ... 

Biogenic nutrient cycling and biogenic mineral production... 

Biomineralization is the process whereby organisms form minerals, and research in this field provides an excellent example at the interface between the earth and life sciences. Early research focussed on biologically formed calcium-containing minerals and the field of calcification was bom (e.g. Schmidt 1924). However, as the diversity of known biogenic minerals has grown, currently 64 different minerals are known (Knoll 2003), the general field of research has become known as biomineralization (Weiner Dove 2003). 

Bradley JP, McSween HY Jr, Harvey RP (1998) Epitaxial growth of nanophase magnetite in martian meteorite Allan HiUs 84001 Implications for biogenic mineralization. Meteorit Planet Sci 33 765-773... 

Ultramicrotomy (see Figure 2) of the resin-embedded material should be performed exclusively with a diamond knife to overcome the hardness of mineral particles or biogenic minerals such as silica frustules, which quickly damage conventional glass knives. 

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