Baria Crystal, known as Bariarite or Variarite (バリアライト Bariaraito) in the Japanese version, is a substance native to Barian World.
At some point, Kite Tenjo acquired a Baria Crystal, which he used as a new power source for Orbital 7. Later, after he and Orbital 7 stole Yuma's key and found that no substance native to Earth could affect it, Kite suggested they try using the Baria Crystal on it. Using it, they successfully opened a portal, allowing Kite to enter the world inside the Key.
Within the chamber where Dumon, Girag, Mizar and Alito meet in Barian World, many of these crystals are present. Before leaving for Earth, Girag crushes one with only his fist. The crystals serve as devices that can be used to monitor Earth. Using them, Dumon witnessed Girag's failures, prompting his decision to send Alito to Earth too.
The crystals also have healing properties, seen when Girag and Alito were resting inside them to heal after being defeated by Yuma.
A Baria Crystal was made as the cocoon of Don Thousand, from which he revealed his true form. 
A Baria Crystal used to unseal the Emperor's Key
Orbital 7 projects a shield powered by his Baria Crystal
Don Thousand's Baria Crystal cocoon.
- Yu-Gi-Oh! ZEXAL episode 02323: "Hunting Down the Hunter, Part 1"
- Yu-Gi-Oh! ZEXAL episode 07474: "Attack of the Barians: Part 1"
- Yu-Gi-Oh! ZEXAL episode 08080: "Rivals in the Ring"
- Yu-Gi-Oh! ZEXAL episode 09494: "Enter Vector"
- Yu-Gi-Oh! ZEXAL episode 135135: "Dragon Strife, Part 2"
- Yu-Gi-Oh! ZEXAL episode 138138: "The New World"