Silver Diamond

Silver Diamonds are the second most valuable treasures in Luigi's Mansion (the first are the Gold Diamonds). Usually, Luigi will find these in green Treasure Chests, along with two Gold Bars, after defeating an optional portrait ghost in the Mansion. This is not possible with an area that does produce a green Treasure Chest after lighting up the room, but not because Luigi sucked up a Portrait Ghost, because there was no Portrait Ghost found in the room, such as the Telephone Room or the Washroom of the second floor. Each Silver Diamond is worth 2,000,000G(s), totalling 10,000,000G(s) in the North American version of the game.

PAL Version
PAL versions of the game are thoroughly different in when playing the Hidden Mansion, as all of the Speedy Spirits and Golden Mice always drop one Silver Diamond when defeated, totalling 30 Silver Diamonds in the whole mansion. Though the player doesn't need to collect every single Silver Diamond to get an A rank, he/she still need to collect the Silver Diamonds to achieve an A. While the goal for an A rank mansion in the PAL versions is 150,000,000G(s), 100,000,000G(s) is needed for the NTSC version. The maximum possible amount to get in the normal mansion alone is 142,390,000G(s). There are maximum total of 5 Silver Diamonds in the entire Mansion, as opposed to the PAL Hidden Mansion, which has a maximum of 30.

Trivia

 * Despite the fact it's the second most valuable treasures in the game, in the PAL Hidden Mansion, collecting all 30 Silver Diamonds result in 60,000,000G(s), greater than two Gold Diamonds, which equal 40,000,000G(s).