Gem

Gemstones are valuable objects found in Luigi's Mansion: Dark Moon. There are thirteen Gemstones hidden in each of the five mansions in the game, making a grand total of sixty five Gemstones 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 Gemstones corresponds to the theme of the five mansions. Unlike the Red, Silver, and Gold Diamonds found in the original game, Gemstones do not function as a form of currency, but rather as a collectible. Once the player has collected all thirteen Gemstones in a mansion, they will be rewarded with one of five different statues of Luigi with the Gemstones encrusted in the stand. The player can see the Gemstones they've 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.

Some Gemstones can be obtained in any mission, while some can only be obtained in a specific mission or once certain conditions have been met.

Amethysts
Once You Collect All Amethysts You Get A Scared Luigi Statue