Abstract

Pearls and shells of some mollusks are attractive inorganic materials primarily owing to the beauty of their natural lustrous and iridescent surface. The iridescent colors can be explained by diffraction or interference or both, depending on the microstructure of the surface. Strong iridescent colors are very evident on the polished shell of the mollusk Haliotis Glabra, commonly known as abalone. It would be interesting to study how these colors are produced on the surface of the shell. By using a scanning electron microscope (SEM), the surface of the shell is found to have a fine-scale diffraction grating structure, and stacks of thin crystalline nacreous layers or platelets are found below the surface. These observations suggest that the iridescent colors are caused by both diffraction and interference. From measurements done on the diffraction patterns that were obtained using a He-Ne laser illuminating the shell, the groove width of the grating structure was derived. Good agreement was found between the derived groove density by diffraction and that measured directly using the SEM. The crystalline structure of the nacreous layers of the shell is studied using Fourier transform infrared spectroscopy and SEM observations. The infrared absorption peaks of 700, 713, 862 and 1083 cm-1 confirmed that the nacre of the shell is basically aragonite. The strong iridescent colors of the shell are the result of high groove density on the surface which causes diffraction. The uniform stacking of layers of nacre below the surface of the shell also causes interference effects that contribute to the iridescent colors.

© 2004 Optical Society of America

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References

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Am. Sci. (1)

D. W. Lee, �??Iridescent blue plants,�?? Am. Sci. 85, 56-63 (1997).

Appl. Opt. (7)

Biomaterials (1)

F. Song, A. K. Soh and Y. L. Bai, �??Structural and mechanical properties of the organic matrix layers of nacre,�?? Biomaterials 24, 3623-3631 (2003).
[CrossRef] [PubMed]

J. Exp. Mar. Biol. Ecol. (1)

T. Baird and S.E. Soloman, �??Calcite and aragonite in the eggshell of Chelonia Mydas L.,�?? J. Exp. Mar. Biol. Ecol. 36, 295-303 (1979).
[CrossRef]

J. of Materials Research (1)

E. DiMasi and M. Sarikaya, �??Synchrotron x-ray microbeam diffraction from abalone shell,�?? J. of Materials Research 19, 1471-1476 (2004).
[CrossRef]

J. of Microscopy (1)

S. Blank, M. Arnoldi, S. Khoshnavaz, L. Treccani, M. Kuntz, K. Mann, G. Grathwohl, and M. Fritz, �??The nacre protein perlucin nucleates growth of calcium carbonate crystals,�?? J. of Microscopy 212, 280-291 (2003).
[CrossRef]

J. Opt. A: Pure Appl. Opt. (1)

A. R. Parker, �??515 million years of structural color,�?? J. Opt. A: Pure Appl. Opt. 2, 15-28 (2000).
[CrossRef]

Materials Science and Engineering: C. (1)

S. Weiner, L. Addadi, and H. D. Wagner, �??Materials design in biology,�?? Materials Science and Engineering: C. 11, 1-8 (2000).
[CrossRef]

Nature (1)

P. Vukusic and J. R. Sambles, �??Photonic structures in biology,�?? Nature 424, 852-855 (2003).
[CrossRef] [PubMed]

Opt. Express (1)

The J. of the Gemmological Soc. of Japan (1)

K. Wada, �??Formation and Quality of Pearls,�?? The Journal of the Gemmological Society of Japan 20, 1-4, 47-56 (1999).

Other (5)

R. D. Barnes, Invertebrate Zoology (Saunders College Publishing, USA, 1986), p. 402�??411.

E. Hecht, Optics, International Edition, 4th Edition (Addison Wesley, USA, 2002) p. 426-428.

N. H. Landman, P. M. Mikkelsen, R. Bieler, and B. Bronson, Pearls, A Natural History (Harry N. Abrams, New York, 2001) p. 23�??61.

K. Nassau, The physics and chemistry of color �?? the fifteen causes of color (John Wiley & Sons, USA, 2001), p. 247�??277.

B. Smith, Infrared Spectral Interpretation - A Systematic Approach (CRC press, London, UK, 1999), p. 31-112, 171.

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Figures (6)

Fig. 1.
Fig. 1.

The polished shell of the mollusk Haliotis glabra has beautiful iridescent colors.

Fig. 2.
Fig. 2.

The typical groove structures on the shell surface, one with fine closely-spaced grooves of about 2–8 μm width and the other with a wider spacing of about 30–50 μm.

Fig. 3.
Fig. 3.

The cross-section of the abalone shell showing a layered microstructure composed of aragonite platelets, separated by a thin layer of conchiolin. The thickness of each nacreous layer is about 0.5 μm.

Fig. 4.
Fig. 4.

Typical diffraction patterns produced by the shell showing: (a) bright spots with higher orders overlapped (b) a set of fine fringes at the zero order position. The average spacing of these fine fringes in the central diffraction band is about an order of magnitude less than the spacing between the main diffraction bands.

Fig. 5.
Fig. 5.

Spectral reflectivity of 1024 composite nacreous layers at various angles of incidence.

Fig. 6.
Fig. 6.

The FTIR spectrum of the nacreous layer of shell with double peaks for the C-O in-plane bends (700 and 713 cm-1), giving evidence for the presence of aragonite.

Tables (2)

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Table 1. Diffraction measurements of narrow grooves on shell surface using He-Ne laser

Tables Icon

Table 2. Diffraction measurements of large grooves on shell surface using He-Ne laser

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