Ice Pearls

As many know, pearls are formed within special oysters when some minute irritant lodges in their sensitive flesh. Over time a hard luminous coating surrounds the irritant, forming a lustrous pearl.  These oysters live in shallow coastal waters, in the salty environs of the seas. With one known, rare exception. The Ice oyster 
The pearl formed by these oysters is both similar to and very different from the more commonly found ones. While pearls can be of any shape when harvested from other oysters, the ice pearls are always elongated, never a perfect sphere. Most of the time they are flattened as well. They are never white, the most common color is some shade of gold or yellow. Those who harvest these orbs feel like they are little bits of the sun, something the oysters are rarely exposed to.
These pearls are very durable, much harder than their warmer, sea-based equivalents. They do not crack, or shatter and they can be carved by someone with the skills to work on something so small and smooth.  They even seem to glow when in dim light.  But the greatest difference these orbs have is their reaction to temperature. They are not ice, but if they get too warm, they will begin to disintegrate.  It is this very weakness that makes them prized among the elite. Great care is taken to ensure they are able to be transported, and only the very wealthy are able to maintain the conditions needed to preserve them.  They must be stored in a cold environment, and when worn as jewelry, it cannot be for extended periods of time, so servants must always be on hand to remove and store them quickly if they are to be preserved.
The very wealthy might make a show of their wealth by deliberately presenting themselves wearing these ice pearls and allowing them to break apart, an evidence that they have resources enough to think nothing of such a loss.
Another unique feature possessed by these pearls is their sound. Because they are so hard, when tapped with a jeweler's hammer they will sound a tone. The sound is not loud, the pearls are small after all, but it can be heard and a master craftsman will use the sound as they assemble pieces of jewelry from them. A necklace or bracelet or anklet made with pearls that are harmonious will always be more beautiful than one where the sound was not taken into account.  It's a closely guarded secret among master artisans.
Because of their rarity, strength, and color there are hardy individuals who will cope with the miserable conditions and eke out a living gathering these pearls.  Most live in the community of Foolshope, a semi-permanent settlement on the Winter River.

Rarity

Very rare. Found only in one small place. The location is small and harsh, the creature that produces these lives only there and is not plentiful, and not every creature produces a pearl.