Amber

Amber was fossilized tree resin and was usually tumbled into smooth stones or polished and cut cabochon.

Description
This fancy stone was soft and brittle and easily worked into strings of beads and used for trade by barbarians of the north. Specimens that contain other fossils, like plants and insects, were priced much higher than the base value. Amber was believed to bring good luck in avoiding disease and plague. A typical specimen had a base value of 100 gp.

Also see

 * Amber items

Sourcebooks

 * Forgotten Realms Adventures
 * Forgotten Realms Campaign Setting 3rd edition