The Chat Gem is a gem that appeared between the game and chat windows on Diablo II Battle.net. Players soon discovered that this gem could be clicked on and would change. The color would change, and when it changed a message would pop up into the chat, stating: "Gem Activated." When clicked once more, it would say: "Gem Deactivated".
On rare occasions, a message would appear (mind you after a LOT of clicking) "Perfect Gem Activated", and other times: "Moooo."
Players soon began to speculate that when the perfect gem was activated, all gems in the current player's inventory would be upgraded to perfect gems. Others said that when activated, all it did was ensure a gem shrine would be placed in the game. When asked, Blizzard replied: "The chat gem is working as intended."
The Chat Gem has made its appearance on Diablo III's web page, although when clicked, it appears to do nothing but turn purple. However, when clicked whilst on the Skill Calculator page, it will create a random build for your currently selected hero. The gem can also be found on Warcraft III's World Map Editor. When clicked, the green gem turns purple with the following message "Gem Activated". Any units deleted after the gem has been activated will display their "death animation" upon deletion.
In an interview at Gamescom 2011 by GameTrailers, Jay Wilson stated that "the chat gem is not coming back" to Diablo III. He also said, "I will definitively say, the chat gem did nothing" in regards to its functionality in Diablo II.