The Crystal Onix (Japanese: クリスタルのイワーク Crystal Iwark) is a rare pokemon 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 in the anime as an inspiration for a little girl, Marissa whose older brother, Mateo who sculpted pokemon from glass. He had lost his drive for sculpting, but he would regain it upon seeing the Crystal Onix.
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.