The GEMS are special bonuses. There are 5 GEMS, each having a different color. They appear as bonuses but their frequency of apparition is the rarest.
Besides, the next GEM that will appear is random defined which makes even more difficult to gather the whole collection.
Separately, they don't have any effects except that a lot of points are granted but once the whole collection has been collected the bonus is simply terrific: The level of game is immediately ended and the player jumps 5 levels in a row or to End if came if he or she was playing at 4 levels below the last. The score receives 50K points. The player receives one extra life and naturally, the all GEMS disappear.