In case you're wondering why I didn't just add the Gems and leave the Plates, it's because then there would be too many items and there will be less chances to find the one you want. Also, once you find a Plate (somewhere else in your game) you will keep it, and Gems are lost after use. In any case, I hope you find this useful. If you add it to your game please credit me and LDEJRuff from DeviantART for the Cover/Plume Fossils. (And obviously Maruno for creating the Mini-Game in the first place).
ehm no. these are "gems".
They are one-use type-enhancing items introduced in Generation V (Pokemon Black and White). There are 17 types of Gems, one corresponding to each of the 17 types. A Gem is consumed when the Pokémon holding it uses a damaging attack that matches the Gem's type; the attack's power is boosted by 50%. The Gem will not be consumed if the attack misses.