Pearl Rotation Inside the Shell

What Causes Pearl Rotation within the Shell? Spey Co. Fine Pearl Jewelry

Those delightfully inquisitive readers of Spey will already know how an oyster makes a pearl (hint: it’s not with a grain of sand), but what makes pearls round? The creation of a pearl is one of the most fascinating defense mechanisms in nature – it is the story of beauty triumphing over adversity. When presented with an irritant or foreign particle that pierces the shell and wedges itself in soft tissue, a mollusk sets to work wrapping layer after layer of rich and satiny nacre around the intruder. This conceals the irritant and in time, forms the lustrous pearl.


Why pearls are round

But why would this natural, organic gem be round? It seems intuitive that the rogue intruder would be anything but round, so how do layers of nacre wrapped around it form a perfect sphere? The truth is, of course, that most pearls aren’t round. In fact, very, very few are. Most pearls that emerge from an oyster are off-round, teardrop, oval, or baroque in shape. As little as 3 to 5 percent of the harvest might be qualified as round. This rarity means that perfectly spherical pearls command higher prices than their more numerous un-round cousins.

Pearls “grow” as each successive layer of nacre is added within the pouch that holds them inside the mollusk. Recent studies suggest that as new layers are added, they release energy, which ever-so-slightly heats the surface. As the structure then interacts with cooler water molecules in the surrounding fluid, a minute thermodynamic reaction takes place. If you hark back to your early science training and the principle of conservation of momentum, you shan’t be too surprised that the resulting force in the opposite direction causes movement. Some scientists even suggest they can quantify the rate of rotation: once every 20 days or so.


Just keep spinning, just keep spinning…

This steady, silent rotation within the mollusk creates the round symmetry lauded in the finest pearls. Often, however, the rotational axis shifts and the resulting pearl spins wonkily. This creates the fascinating off-round pearl shapes that can be just as alluring in decadent pearl jewelry. We at Spey love all pearls of great quality, whether they be perfectly round and exquisitely matched, or baroque in shape and one-of-a-kind. What’s your pearl style?