Sciencemadness Discussion Board

Color inside seashells

morsagh - 1-1-2016 at 18:59

Some time ago i found big seashells, so i took them home and tried to wash with just water with normal liquid soap. Now i noticed that my washbasin is very nice colorful shining like something between milky and precious opal, nice soft green to red colors like you can see inside some seashells. My question is what is chemical compound causing this nice color efect?

Amos - 1-1-2016 at 21:03

The substance is called nacre, and is composed of thin sheets of a mineral form of calcium carbonate called aragonite. These sheets are coincidentally about the same thickness as the wavelengths found in the visible light spectrum, causing them to interfere with the colors of light that reflect back off at a given angle, otherwise known as iridescence.
Source: Wikipedia

Ordinarily I'd greet a post like this with a suggestion to go use google, but this was too fascinating to pass up.

morsagh - 1-1-2016 at 21:48

Sorry i was searching but nothing found. Can be this synthetized? Maybe oil-colloid of CaCO3 by thermal decomposition of HCO3 salt (just strong guess)?

Hawkguy - 2-1-2016 at 18:05

I could be wrong, but I'm pretty sure the shellfish accumulate the layers over long periods of time. To recreate this effect would mean trying to mimic a biological process by depositing ultra thin layers of the material on whatever. Also sure that this would be very difficult to replicate in a home lab setting, trying to deposit the carbonate would likely just give you a cake, without the nice layers.