The Crystal Onix (Japanese: クリスタルのイワーク Crystal Iwark) is a rare Pokémon found only on the Orange Islands (in the anime). It is made of Crystal due to eating the diamonds formed in the cave in which it lives.
It earned a name for itself, but only as a myth. The Crystal Onix appered as an inspiration for a little girl, Marissa, whose older brother, Mateo, sculpted Pokémon from glass. He had lost his drive for sculpting and went to a quest to capture the Crystal Onix. He battled it using Cloyster, but was soon defeated. He attempted with Charmeleon, but upon seeing its strength, Mateo decided to leave it, as it got his inspiration up.
+ indicates this Pokémon used this move recently.* - indicates this Pokémon normally can't use this move.
Despite Onix originally being a Rock/Ground type with a weakness against water, the Crystal Onix simply ignores Water-type attacks and they bounce off its skin but Fire-type attacks seem to be super-effective against it.
As with all the other Onix in the series, the Crystal Onix is voiced by Unshō Ishizuka in both the Japanese and English-language versions.