A Runed Amethyst is an enchanting crystal that can be used on an enchanted forge on any enchantable item. This gem will modify any weapon to deal acid damage on subsequent turns after a successful hit, as well as modify any armor to have a 5% increase in acid and poison resistance.
This item was introduced in Geneforge 3 and has stayed in the game ever since. The value of a Runed Amethyst is 400 coins yet since the sale price is 1/8th of the value, merchants will buy the item for 50 coins. Often, people accidentally confuse the Runed Amethyst with the Runed Ruby. This is because of the similar name and icon.