Centuries, or the most expensive jewelry in the world wasn't made of diamonds, rubies, or emeralds.

Rather, they were made with an extremely rare substance that was occasionally found inside of clams and oysters.

Pearls. Pearls.

Pearls were so valuable that they could only be possessed by kings, queens, and emperors.

Today, the manner in which pearls are made is pretty much the same,

but they're more common now than at any point in history.

Learn more about pearls, how they're made and how they've been harvested throughout history,

on this episode of Everything Everywhere Daily. Some of the most valuable substances in the world are gemstones.

Gemstones are pieces of mineral that form a crystal lattice at the atomic level.

Diamonds, rubies, sapphires, and emeralds are examples of such crystalline minerals.

However, there are some gemstones that are not crystals at all, but are still considered to be very valuable.

Opals are an example of something that's considered to be a gemstone but do not have a crystalline structure.

Amber is often classified as a precious gem,

but it's really just fossilized tree sap.

However, there's one substance that is neither a crystal nor a fossil,

and it's continually produced by

organic means in many parts of the world. Pearls are unlike any other gemstone

in that they're harvested from a living organism not mined from the earth.

So what exactly is a pearl and what makes pearls so different?

Pearls come from mollus, in particular two different types of bivalves, the salt water pearl

oyster and the freshwater pearl clam. However, it is possible for a pearl or pearl-like object to appear in any type of mollusk with a shell.

Pearls are created when an irritant, usually a small piece of shell or a grain of sand,

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