Hark! The flame of pearls, the pearl on fire, the flame structure of pearls! You will only get the flame of pearls in non-nacreous pearls. Tell me, do you know what a non-nacreous pearl is? Well, read all about them here!
Here is the brief run-down: Gorgeous, lustrous, nacreous pearls are composed of mostly aragonite. Fabulous, porcelain-like, non-nacreous pearls are made, primarily, of calcite. Both aragonite and calcite are calcium carbonate but with different crystalline structures meaning they reflect and refract light differently.The calcite simply has a lower luster than the aragonite. Boom! There it is.
Now, typically you want nacreous pearls. They are the gorgeous pearls we think of when we think about pearls! But non-nacreous pearls can be interesting, too. They can also be valuable. Read up on my post, When Non-Nacreous Pearls Have Value.
But here is something cool that non-nacreous pearls have that nacreous pearls cannot have. Sure, nacreous pearls have the luster but non-nacreous have the potential flame of pearls. This is a flame structure created by the intersection of calcite with aragonite. This is an optical phenomenon meaning an event that results from the interaction of light and matter. Something like a rainbow, a halo or even a mirage. This optical phenomenon makes the non-nacreous pearl almost look like it is alive! Here are some example of a flame structure in a conch pearl.
Truly stunning to look at and, again, only possible in a non-nacreous pearl!