Growth mineral phase

Spanos, N. and Koutsoukos, P.G., 1998. The transformation of vaterite to calcite effect of the conditions of the solutions in contact with the mineral phase. Journal of Crystal Growth, 191, 783-790. 

The geochemical fate of most reactive substances (trace metals, pollutants) is controlled by the reaction of solutes with solid surfaces. Simple chemical models for the residence time of reactive elements in oceans, lakes, sediment, and soil systems are based on the partitioning of chemical species between the aqueous solution and the particle surface. The rates of processes involved in precipitation (heterogeneous nucleation, crystal growth) and dissolution of mineral phases, of importance in the weathering of rocks, in the formation of soils, and sediment diagenesis, are critically dependent on surface species and their structural identity. 

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. 

Geometry , time scale and length scale are thus key factors in assessing possible modes of transport of the mineral phase components. The chemical state of the medium from which the mineral forms, and its nucleation and growth processes, are other key factors in determining the final properties of the mineral. These will be discussed below. 

Figure 7 The growth of the Sr/ Sr ratio over time for the major mineral phases of a granitic rock. Note the much smaller growth rate for feldspars compared to mica. The feldspars contain the hulk of the strontium in such a rock and control the isotopic composition of the saline waters (McNutt et al., 1990) (reproduced hy permission of Elsevier from Geochim. Cosmochim.

While the initial stage of iron incorporation in mammalian ferritins requires the ferroxidase sites of the H-chains, thereafter the inner surface of the protein shell of the L chains provides nucleation sites which supply ligands that can partially coordinate iron but which leave some coordination spheres available for mineral phase anions. This enables the biomineralisation process to proceed, with formation of one or more small polynuclear ferrihydrite crystallites, which can then act as nucleation centres for mineral growth. Most probably, one of these clusters will become the dominant nucleation centre and growth of the mineral would then occur from this centre. 

The diagram in Figure 4.15 emphasizes the continuity of precipitation and coprecipitation processes with chemisorption, both in time and space. Low levels of adsorbate (whether metal cations or anions) are usually bound by chemisorption, higher levels by the formation of sohd solutions or by the nucleation of small adsorbate clusters at surfaces. The highest levels of adsorbate lead to precipitation of separate mineral phases, a process that can be viewed as an extension of cluster growth that allows a new solid phase to become detectable. 

Fig. 2. Low and high resolution maps of polysaccharides distribution in the Goniastrera skeleton (a) Polished surface of wall and septa (b) Low resolution X-ray fluorescence map higher concentrations of S-polysaccharides are visible in EMZ of wall and septa (c) High resolution X-ray fluorescence map in fibrous tissue. Evidence of the layered distribution of S-polysaccharides (d) Banding pattern within the mineral phase. Correspondence between mineral stepping growth and layered distribution of polysaccharides indicates that the two phases (organic and mineral) interplay at a submicrometre scale.

Cahill CL, Benning LG, Barnes HL, Parise JB (2000) In situ time-resolved X-ray diffraction of iron sulfides during hydrothermal pyrite growth. Chem Geol 167 53-63 Cahill CL, Benning LG, Norby P, Clark SM, Schoonen MAA, Parise JB (1998) In situ X-ray diffraction apparatus and its application to hydrothermal reactions of iron sulfide growth and phase transformations. Mineral Mag 62A 267-268... 

The steep concentration profiles seen in many fossil bones, particularly those from terrestrial environments (e.g.. Fig. 4), indicate that fossil bones often do not reach equilibrium in terms of metal partitioning, despite millions of years of potential exchange with groundwaters. Evidently exchange with groundwaters is halted, presumably by growth of authigenic mineral phases and reduction of porosity. 

Fig. 3.9 A, B. Schematieai representation of the free energy states and the activation energy barriers for mineralization. Pathway A, crystallization of a mineral phase from pure and impure solution (with no major structural modifications) pathway B, formation of a crystalline mineral from intermediate phases of different crystal structure. AGn, free energy of nucleation AGg, free energy of growth AGx, free, energy of phase transformation...

Note that if precipitation proceeds via pathway B of Fig. 3.9, and the final mineral is crystalline, then nucleation vnll not be a determining factor in the crystallographic structure of the final mineral since the initial phase is amorphous. In such cases mineral structure will be dependent on biological control (chemical and/or organic matrix-mediated) over mineral growth and phase-transformation processes. 

The mineral phase is mainly formed by calcium and phosphorous, which form spindle- or plate-shaped crystals of HAp [3Ca3(P04)2.(0H)2]. HAp nanocrystals of bone locate at hole zones within the collagen fibrils. This restricts the possible primary growth of the crystals and forces them to be discrete and discontinuous. The mineral crystals grow with a specific crystalline orientation. The c-axes of the... 

This communication provides the first experimental evidence of biologically produced crystalline silica mineral phase (i.e., chalcedony) and its growth (crystallinity) in electric organs from living electric fish. 

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