Force Gem
Force Gems appear in Four Swords Adventures. Throughout each level, found on enemies, under rocks, frozen in ice, and more. You need to collect (2000) of them. Once you have, the Four Sword will become empowered, and you can break Vaati's Dark Barrier at the end of each level. They come like Rupees in the game, the size of them and color determines how much you get. (Such as, getting a small Red Force Gem is more valuable than a small Green Force Gem) Often in levels, there will be an area that allows an opportunity to get many at once, mostly, these are defeating many enemies without being hit. Doing this awards combo points, which will give more Force Gems when you defeat the enemies or lose your points. Beware though, because Tingle is in the game. After you find him under a rock, he will come when you usually find a big Force Gem or many. He attempts to steal one. You can throw a rock or enemy at him, but for humor, you can throw one of your friends at him.
Force Gems return in Phantom Hourglass. They are used in The Temple of the Ocean King and are an integral part of multiplayer Battle Mode. In the temple, they are used to complete a Triforce symbol in the ground that will open a door. The door usually brings the player to a checkpoint in the dungeon. Oshus explains early in the game that the Force Gems are made of Sand of Hours. These are all Gold colored. Link slows down considerably while holding one!
The Battle mode force gems vary in size. The colors are changed during gameplay but the value of points remain the same. The larger it is, the more it is worth and heavier to carry.