Emeralds

Emeralds are a special form of gems, which are especially sought after because of their vivid green color. It's their rarity that makes them so precious.

Description
In the valley of Eodon, the Nahuatla Tribe was the only tribe to engage in modern trading with a monetary system, having decided to make emeralds their currency. During their stay however, the Avatar hadn't had much chance to take advantage of this economy, due to the current political situation in the city. Only one vendor actually did business. Aside from finding emeralds, the weaver Paxaptamac paid the Avatar with one emerald for 10 parrot feathers, and the weaponmaker Atlipacta accepted them for her goods, with prices from one to three emeralds for one weapon or bundles of ammunition.

Trivia

 * There is a vending machine which gives chilled fruit for the price of emeralds in the ancient city of Kotl. Either the Kotl had a really huge supply of emeralds, or inflation was a huge problem at these times.
 * Emeralds are also known in Britannia, as evidenced by the name of the tavern of Cove in Ultima VII: The Emerald.