Gold Diamond

Gold Diamonds are the most valuable treasures in Luigi's Mansion, worth 20,000,000G each. There are two in the game: Luigi must water a plant three times in the Boneyard (where Spooky resides): once when he first sees it, once after defeating Bogmire, and once after defeating Boolossus to make the now-flower bloom, revealing the diamond. The other can be found if Luigi captures all 50 Boos (not counting King Boo); the last Boo will drop the treasure right in front of him. If Luigi wants a good mansion to live in, he should collect both Gold Diamonds. If Luigi dies or quit the game after getting the second Gold Diamond from the last Boo, this diamond will disappear from Luigi's inventory.

They are significantly larger than Blue Diamonds and Red Diamonds.