In the original Crash game, where the colored gems were earned on the same way as the clear gems, the Green Gem is obtained by breaking all the boxes in The Lost City. It opens up the Green Gem Paths in Jungle Rollers and Castle Machinery.
The Green Gem appears a bit flat and oblong. In this game, it can be obtained in The Eel Deal by completing the secret course behind a fake wall. It opens up the Green Gem Route in Ruination and part of the Multicolour Gem Route in Spaced Out.
The sprite of the Green Gem is exactly the same as in Crash 2. It can be obtained by completing the Death Route in Flaming Passion. It opens up the Green Gem Route in Gone Tomorrow and part of the Multicolour Gem Route in Bug Lite.
The gems awarded in Crash Bash are all green. Each minigame contains a green gem and it can be won by winning a harder version of this mini game. It takes 25 gems unlock the level Keg Kaboom.