Amber

Amber is a Gem. Besides Orange Torches and Amber Gemspark Blocks, Amber cannot be used to make anything else the other gems can be made into, such as Grappling Hooks or Phaseblades, although it can be placed as a decoration like the other gems.

Unlike other gems, amber cannot be mined, and can only be acquired by feeding silt and slush to an Extractinator.

Trivia

 * Amber's only purpose (Excluding Gemspark Blocks.) is to craft Orange Torches which was added upon request of a "really persistent nagging brit." aka James Bennett (ChippyGaming) http://www.youtube.com/chippygaming a Youtuber who makes Terraria videos among other things.