Tag Archives: nacrem mother of pearl. iridescence

Clues as to how mother of pearl is made

Iridescence seems to fascinate scientists and a team at Cornell University is no exception (from a Dec. 4, 2015 news item on Nanowerk),

Mother nature has a lot to teach us about how to make things.

With that in mind, Cornell researchers have uncovered the process by which mollusks manufacture nacre – commonly known as “mother of pearl.” Along with its iridescent beauty, this material found on the insides of seashells is incredibly strong. Knowing how it’s made could lead to new methods to synthesize a variety of new materials with as yet unguessed properties.

“We have all these high-tech facilities to make new materials, but just take a walk along the beach and see what’s being made,” said postdoctoral research associate Robert Hovden, M.S. ’10, Ph.D. ’14. “Nature is doing incredible nanoscience, and we need to dig into it.”

A Dec. 4, 2015 Cornell University news release by Bill Steele, which originated the news item, expands on the theme,

Using a high-resolution scanning transmission electron microscope (STEM), the researchers examined a cross section of the shell of a large Mediterranean mollusk called the noble pen shell or fan mussel (Pinna nobilis). To make the observations possible they had to develop a special sample preparation process. Using a diamond saw, they cut a thin slice through the shell, then in effect sanded it down with a thin film in which micron-sized bits of diamond were embedded, until they had a sample less than 30 nanometers thick, suitable for STEM observation. As in sanding wood, they moved from heavier grits for fast cutting to a fine final polish to make a surface free of scratches that might distort the STEM image.

Images with nanometer-scale resolution revealed that the organism builds nacre by depositing a series of layers of a material containing nanoparticles of calcium carbonate. Moving from the inside out, these particles are seen coming together in rows and fusing into flat crystals laminated between layers of organic material. (The layers are thinner than the wavelengths of visible light, causing the scattering that gives the material its iridescence.)

Exactly what happens at each step is a topic for future research. For now, the researchers said in their paper, “We cannot go back in time” to observe the process. But knowing that nanoparticles are involved is a valuable insight for materials scientists, Hovden said.

Here’s an image from the researchers,

Electron microscope image of a cross-section of a mollusk shell. The organism builds its shell from the inside out by depositing layers of calcium carbonate nanoparticles. As the particle density increases over time they fuse into large flat crystals embedded in layers of organic material to form nacre. Courtesy: Cornell University

Electron microscope image of a cross-section of a mollusk shell. The organism builds its shell from the inside out by depositing layers of calcium carbonate nanoparticles. As the particle density increases over time they fuse into large flat crystals embedded in layers of organic material to form nacre. Courtesy: Cornell University

Here’s a link to and a citation for the paper,

Nanoscale assembly processes revealed in the nacroprismatic transition zone of Pinna nobilis mollusc shells by Robert Hovden, Stephan E. Wolf, Megan E. Holtz, Frédéric Marin, David A. Muller, & Lara A. Estroff. Nature Communications 6, Article number: 10097 doi:10.1038/ncomms10097 Published 03 December 2015

This is an open access paper.