Gem

Gems, also referred to as gemstones, are valuable objects found in Luigi's Mansion: Dark Moon and Luigi's Mansion 3. They bear a resemblance to Stones from the preceding game, Luigi's Mansion, though these items serve as collectibles rather than containing a value of gold. In Luigi's Mansion: Dark Moon, there are thirteen gems hidden in each of the five mansions in the game, making a grand total of 65 gems in the entire game. Amethysts are found in Gloomy Manor, emeralds are found in Haunted Towers, rubies are found in Old Clockworks, sapphires are found in Secret Mine, and diamonds are found in Treacherous Mansion. The coloration of the five sets of thirteen gems corresponds to the theme of the five mansions. Some gems can be obtained in any mission, while some can be obtained only in a specific mission or once certain conditions have been met.

Once the player has collected all thirteen gems in a mansion, they will be rewarded with one of five different statues of Luigi with the gems encrusted in the stand. The player can see the gems they have collected inside the Vault, on the mansion select screen, when one is collected in a mansion, and when the totals and records are displayed at the end of a mission. Any statues that have been unlocked can only be viewed inside the Vault.

In Luigi's Mansion 3, there are six gems on each floor: one white, one red, one blue, one green, one purple, and one yellow. The gems will be a different shape depending on the floor. They are shaped like cubes in the Basement, diamonds in the Grand Lobby, rectangular prisms in the RIP Suites, ovals in the Mezzanine, teardrops in the Hotel Shops, quavers in The Great Stage, swords in Castle MacFrights, flowers in the Garden Suites, film reels in Paranormal Productions, dinosaur claws in the Unnatural History Museum, wrenches in the Boilerworks, snakes in the Tomb Suites, dice in the Twisted Suites, skulls and crossbones in The Spectral Catch, dumbbells in the Fitness Center, headphones in The Dance Hall, and King Boo in the Master Suite.

Once all the gems are collected on all floors, the player unlocks Suction Shot Type-B.

9 (Unnatural History Museum)
All six gems are found in the Elevator Hall.

Luigi's Mansion: Dark Moon

 * Instruction manual bio: "If you collect all the gems, something neat may happen!"