How Pearls Form
A pearl is a lustrous orb of calcium carbonate produced by many species of shelled mollusks, and is the only known gemstone in the world that comes from a living organism. Due to its beautiful opaque gleam and rarity, this beloved gemstone has been used in jewelry since the 5th Century BC. Oh, and if you were born in June, your birthstone would be a pearl. If you ever wondered how these wonders of nature are formed, I’ll explain the step-by-step processes in the article below.
Pearls, as beautiful as they are, actually serve as a defensive mechanism for shelled mollusks against any irritants (i.e. parasite, debris) that enter within the shells. A simplified explanation of how a pearl is formed is basically that when a foreign material enters, the organism would form a ‘pearl sac’ that engulfs the aforementioned material– this pearl sac is composed of a combination of calcium carbonate and conchiolin, a complex protein secreted by a shelled organism’s mantle. (you can see for yourself what the mantle looks like in our dissection video here). The process described would repeat many times, and the organism coats the irritant in the calcium carbonate/conchiolin film (referred to as a nacre), layer after layer until a sizable pearl is formed.
It is important to note that the process described above is only for natural pearls, pearls produced in nature without any human interference. However, since natural pearls are very rare, most of the commercially available pearls now are cultured pearls. The process of producing cultured pearls is very similar to the process of natural pearl formation, with the only difference being that the irritant is a surgically implanted lab-produced bead. One downside of cultured pearls is that it takes a staggering three years for a significant amount of nacre to deposit on the bead.
Finally, a third way “pearls” can be formed is through a procedure where a glass bead is dipped in a solution made from fish scales, giving the bead a pearl-like appearance. “Pearls” produced this way are called imitation pearls, and they generally lack in luster in comparison to natural or cultured pearls. One quick way to test whether a pearl is real (natural, cultured) or fake (imitation) is by running your teeth along the surface of the pearl. A real pearl would give you a rough texture due to the layers of nacre on the surface, while a fake pearl would be completely smooth.
Photo credit: https://www.thestreethawker.com/tsh-junior/2017/2/23/how-are-pearls-made-oreos-discovery