What are some natural, but man-facilitated types of jewels?

I’m writing a short story and looking for some examples of types of precious items, such as jewels, that are either largely man-made, such as Venetian Glass, or pearls—the latter being oyster-made, but with modern aqua-farming, something that people facilitate. Both items find their way into wearable jewelry or other precious items. Can anyone think of other types of labor intensive products that end up as jewelry or other luxury items, for example, caviar?