Viridian crystal

Viridian crystals, colloquially known as fool's emeralds, was a crystal found in the Underdark and underground locations in the Western Heartlands.

Description
Viridian crystals were known for being hard to work with because of their brittleness. Its crystalline form was sharp-edged.

Powers
Even though sometimes used for decoration and crafting, fool's emeralds had some alchemical properties.

Appearances

 * Video Games
 * Baldur's Gate III