Crystal Onix is a special Pokemon. It can be found on Route 14, near Flouroma City.
The Crystal Onix appears blue and lets out a crystal barrage while spawning. This indicates that it is indeed a Crystal Onix. What many consider convenient is the fact that it can spawn right where another extremely rare Pokemon spawns; The Beldum (Which evolves to Metang and Metagross). This makes the spot desirable for searching for rares.
Warning: SAVE after obtaining the Crystal Onix. You cannot encounter another one by rejoining, for it isn't a Pokemon you can repeatedly find like Volcanion, Jirachi, Victini, etc. It's a Wild Pokemon, and not only that, it is single-handedly one of the rarest Pokemons in Pokemon Brick Bronze at the moment. If you encounter this, consider yourself lucky. It is desirable in trading. Many offer Pseudo-Legendaries for it.
Rarity: 1/1600 (0.0625%)