Perfectly Pearly

Perfectly Pearly

Pearls are really pretty, and, although I am not one to wear them, my grandmother is. Besides their obvious beauty, they are considered a valuable gem, and are used often in jewelry. But very little people actually know how they are made.

I for one, can initially only tell you without looking anything up that they are often made when a clam gets a piece of sand in its shell and the pearl develops from there. But there is so much more information than just that. So let’s dive a little deeper into the making of a pearl!

My friend Dhara wrote in her blog post that pearls start forming when an oyster gets hurt. She writes, “When a pearl oyster gets hurt, it forms a “pearl sac” to contain the injury. In this injured area, the oyster creates two proteins called conchin and perlucin which form together a matrix called conchiolin,containing many porous spaces similar to a sponge.” In the porous areas, aragonite crystals are secreted and combine with the conchilin to form the pearly substance. After many layers are formed, it becomes a mature pearl!

One substanc ein particular is important. It is called nacr, and is also called “mother of pearl”. This is the “…naturally-occurring organic/inorganic composite, that is a combination of crystalline and organic substances that form the iridescent inner lining of the shell.” In certain species of mollusk, specialized cells called epithelial cells produce nacre. These are toward the outside, while stratified columnar epithelial cells occur toward the center. The nacre is usually put toward the center of the mollusk, creating a nacerous layer, which smooths the inner wall of the being. This serves as a defense mechanism. 95% of nacre is calcium carbonate (CaCO3). One site writes, “This mixture of brittle nanometer platelets and the thin layers of elastic biopolymers makes the material strong and resilient. Strength and resilience are also likely to be due to adhesion by the “brickwork-like” arrangement of the platelets, which inhibits transverse crack propagation.”

Natural pearls can be made around any substance that gets into the shell, like parasites or food. A pearl is created only when this invader can’t be ejected, and starts encystation in the layers of substances mentioned above. These pearls take many, many years to form due to all the layers.

However, there are two different types of pearls. One is the natural kind I have just described, and the other cultured pearls. The main difference is the thickness of the layers in which the pearl is formed. 2 to 5 years is the average time a good quality pearl takes to make. Lower quality pearls are often made faster by inserting a nucleus and speeding up the development of these layers. however, the layers are thinner, and more brittle. In addition, they aren’t as shiny, and won’t last as long.

Pearls are formed as a defense mechanism for an animal with what looks vulnerable behind their shells. Just think, my grandmother’s pearl necklace just got a whole lot more interesting!

Links:

http://www.allaboutgemstones.com/pearl_composition.html

http://captainchemistry.tumblr.com/post/75316059271/relate-with-chemistry-pearls-in-oysters

So ta ta for now and I hope to see your chemical reaction soon!