**4. Conclusion**

294 Advances in Crystallization Processes

These images were obtained of the same crystal from Fig. 7. Cyan colour nanocrystals are

laser was used with emission band in 458 nm (cyan) and 514 nm (yellow). Both nanocrystals are very different. Nanocrystals in cyan colour are acicular in shape. Nanocrystals in yellow are trapezohedral in shape. Quartz and moganite were detected by using ion lasers with

Fig. 9. 3D images of silica polymorphs nanocrystals from the microsomal fraction in LSCM.

The chalcedony crystal has autofluorescence with different ion lasers: a He/Ne ion laser with emission band in 543 nm (red); a He/Ne ion laser with emission band in 633 nm (blue);

acicular (pinacoid) in shape and nanocrystals in yellow are trapezohedral in shape.

different emission bands.

The origin of chalcedony (SiO2) has been widely discussed in the literature. Biomineralization by silica can occur under a wide variety of circumstances (Heaney, 1993; Fernández López, 2000; Nash & Hopkinson, 2004). A slight oversaturation of silicon is necessary for allowing chalcedony formation from the solution.

A crystal is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions (Hahn, 2002). Crystal habit depends on two main factors: the inner, crystalline structure determines the faces the crystal can present; growth conditions, however, determine the relative size of each face, and hence also the overall shape (Rasmuson, 2009).

The conditions at which silica formation occur is at a pH 7 or near a pH of 8 and an Eh (oxidation potentials) of 0.0 to -0.2 (Fig. 10; Krumbein & Garrels, 1952). It was documented oxidative stress in electric organs from Rajidae family fish (Prado Figueroa, 2005). In such oxidative conditions, the presence of iron could contributed to silica formation.

Crystal growth is a major stage in the crystallization process, and consists in the addition of new atoms, ions, or polymer. Details of the early stages of chalcedony genesis are not fully understood but could involve either the direct precipitation of amorphous silica from a hydrous fluid, which then evolves into chalcedony, or the direct growth of crystalline chalcedony (Moxon & Carpenter, 2009).

The proportion of moganite decreases with age (Moxon, 2004; Moxon & Carpenter, 2009). There is a correlation of crystallite growth with moganite content. The recrystallization of moganite to alfa-quartz clearly occurs at the same time as crystallite growth. Water has an important role: In the absence of water vapour, crystallite growth and transformation of moganite to quartz ceases (Moxon & Carpenter, 2009). Moganite is abundant in arid environment, this is probably due to the lack of water available to support the dissolution of moganite and the simultaneous precipitation of quartz (Bustillo, 1992).

The Growth of Chalcedony (Nanocrystalline Silica) in Electric Organs from Living Marine Fish 297

It is possible to identify the silica polymorph components of chalcedony: quartz and moganite in 3-D images of nanocrystals, by using a Laser Scanning Confocal Microscope and Leica software, see Fig. 7. These quartz and moganite nanocrystals can be differentiated by using an argon ion laser with two emission bands: 514 nm (yellow emission) and 458 nm (cyan emission). These are shown at the Figs. 7 to 9. These figures perhaps show the growth

Quartz is estimated to occupy circa 12 % of the earth's crust, so it is not surprising that research into its diverse applications has been of major interest for over 100 years. Important uses are made of quartz minerals that range from piezoelectric devices to the literal downto earth quartz aggregates required by the construction industry. During the past (1950's and 60'0s, there were commercial demands for quality quartz crystal required in the manufacture of medical and aerospace sensors (Moxon, 2004; Moxon & Carpenter, 2009).

Of the intriguing topics that are receiving renewed attention nowadays, the study of the "triangle" biomineralization/demineralization/remineralization is among the most

Electric organs of the electric fish have constituted the choice model for studying the nervous cholinergic system (see: Changeux, 1981; 2010). This chapter shows the autofluorescent chalcedony in electric organs. Autofluorescent chalcedony was also documented in human brains from elderly patients (Prado Figueroa & Sánchez Lihón, 2010). There are many similarities in the occurrence of biosilicification in both systems. One of the major neurochemical features of Alzheimer's disease is the marked reduction of nicotinic acetylcholine receptor in relevant diseased brain regions such as the cerebral cortex and hippocampus (Oddo & LaFerle, 2006). An important use of chalcedony crystals from electric

This paper has demonstrated, using different samples of electric organs, the way Laser Scanning Confocal Microscope with three dimensional (3D) images obtained by using a Leica Confocal Software can be employed to identify chalcedony and nanocrystalline silica

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

This research was partially supported by grants to María Prado Figueroa from Secretaría General de Ciencia y Técnica, Universidad Nacional del Sur (UNS), Bahía Blanca, Argentina. MPF is grateful to Dr. T. Moxon, 55 Common Lane, Auckley, Doncaster DN93HX, UK, for

MPF is grateful to Prof. F.J. Barrantes, ex-Director of the Centro Científico Tecnológico Bahía Blanca, Argentina (CCT-BBca, CONICET - UNS) for his permanent interest in this study.

MPF appreciate Lic. E. Buzzi and Mr. M. Diestefano from the CCT-BBca, CONICET – UNS, for technical assistance. Finally, the author is very grateful to Lic. M. Salaberry, English

of chalcedony in the electric organ from marine fish.

organs is, maybe, in relation with the human medicine.

polymorphs (quartz and moganite) in electric organs from marine fish.

many interesting suggestions about chalcedony formation and isolation.

fascinating (Ehrlich *et al*., 2010).

organs from living electric fish.

Translator, for her excellent work.

**5. Acknowledgment** 

The change in composition of internal water is proposed as a method for approximate dating of agates (a variety of chalcedony) (Moxon, 2004). It has been demonstrated in geological environments that less stable silica polymorphs appear to have transformed over time to chalcedony and microquartz (Nash & Hopkinson, 2004).

Fig. 10. Chalcedony formation. Krumbein, W.C., Garrels, R.M., (1952).

It is possible to identify the silica polymorph components of chalcedony: quartz and moganite in 3-D images of nanocrystals, by using a Laser Scanning Confocal Microscope and Leica software, see Fig. 7. These quartz and moganite nanocrystals can be differentiated by using an argon ion laser with two emission bands: 514 nm (yellow emission) and 458 nm (cyan emission). These are shown at the Figs. 7 to 9. These figures perhaps show the growth of chalcedony in the electric organ from marine fish.

Quartz is estimated to occupy circa 12 % of the earth's crust, so it is not surprising that research into its diverse applications has been of major interest for over 100 years. Important uses are made of quartz minerals that range from piezoelectric devices to the literal downto earth quartz aggregates required by the construction industry. During the past (1950's and 60'0s, there were commercial demands for quality quartz crystal required in the manufacture of medical and aerospace sensors (Moxon, 2004; Moxon & Carpenter, 2009).

Of the intriguing topics that are receiving renewed attention nowadays, the study of the "triangle" biomineralization/demineralization/remineralization is among the most fascinating (Ehrlich *et al*., 2010).

Electric organs of the electric fish have constituted the choice model for studying the nervous cholinergic system (see: Changeux, 1981; 2010). This chapter shows the autofluorescent chalcedony in electric organs. Autofluorescent chalcedony was also documented in human brains from elderly patients (Prado Figueroa & Sánchez Lihón, 2010).

There are many similarities in the occurrence of biosilicification in both systems. One of the major neurochemical features of Alzheimer's disease is the marked reduction of nicotinic acetylcholine receptor in relevant diseased brain regions such as the cerebral cortex and hippocampus (Oddo & LaFerle, 2006). An important use of chalcedony crystals from electric organs is, maybe, in relation with the human medicine.

This paper has demonstrated, using different samples of electric organs, the way Laser Scanning Confocal Microscope with three dimensional (3D) images obtained by using a Leica Confocal Software can be employed to identify chalcedony and nanocrystalline silica polymorphs (quartz and moganite) in electric organs from marine fish.

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.
