**1. Introduction**

Research of nano-size phases through electron microscopy and especially through high reso‐ lution electron microscopy enables to observe the morphology of each nano-sized crystal or short range ordered phase, that are usually not detected by other methods. Moreover, lattice fringes of the precursor and the product differ from each other but the original crystal size and morphology remain. The main object of this chapter is to demonstrate the advantages of using electron microscopy in detecting recrystallization processes and possible identification of the precursors.

Nano sized iron oxides are very common minerals in various environments. Various phases of iron oxides crystallize in natural environments of rocks, sediments and soils. Some of the iron oxides form directly either from melts or from solutions; others are formed by recrystal‐ lization processes of a precursor through dehydroxylation, dissolution/reprecipitation, oxi‐ dation or aggregation involving internal rearrangement within the structure of the precursor. Another formation pattern involves recrystallization of iron-bearing minerals crystallized under anaerobic conditions which are exposed to air. The Fe2+ of these iron bear‐ ing minerals is then oxidized and hydrolyzed into iron oxyhydroxides.

By using a high resolution electron microscopy, the morphology of newly formed iron ox‐ ides can be observed. Moreover, in some cases it is also feasible to detect the precursor's morphology. The newly formed end products are identified by electron diffraction and their chemical compositions are obtained by point analyses; hence, impurities that result from the initial phases can be detected. In most of the samples presented in this chapter, the fine frac‐ tion was checked with a High Resolution Transmission Electron Microscopy (HRTEM) us‐ ing a JEOL FasTEM 2010 electron microscope equipped with a Noran energy dispersive spectrometer (EDS) for microprobe elemental analyses. Other pictures were obtained using

© 2013 Taitel-Goldman; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

a scanning electron microscope JEOL, JXA-8600 and a High Resolution Scanning Electron Microscope Sirion.

**2. Results and discussion**

0.25nm. (Figure 2).

Short range ordered 2-line ferrihydrite (Fe5HO8\*4H2O) is one of the precursors of other iron oxides. It initially precipitates due to Fe2+ oxidation and its crystal growth is hindered by the presence of silicate or soil organic matter. Its structural inner order can clearly be visible in HRTEM images. A selected area electron diffraction pattern shows 2 bright rings at 0.15 and

Recrystallization Processes Involving Iron Oxides in Natural Environments and *In Vitro*

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**Figure 2.** a) High resolution images of short range ordered ferrihydrite preserved within halite crystals in the hypersaline environment at the Dead Sea. The initial stage of recrystallization into a stable phase can be observed at the lower part of the image. Two bright rings at 0.15 and 0.25nm in SAED were obtained. b) A short range ordered pat‐

tern was observed in other crystals of ferrihydrite.

The iron oxides studied were found in various natural environments (Figure 1) including:


Other phases were synthesized in a NaCl solution under varying conditions.

**Figure 1.** a) Middle East map with Atlantis II Deep located in the Red Sea. b) Israel map with location of Mt. Sedom near the Dead Sea and Judean hills. Samples were also collected along the Mediterranean Sea coast.
