Granite

Location
Granite is visible in the town of Kolima, fenced in a small enclosure next to one of the tree-houses, and you cannot reach it from the outside. To reach it, go behind the tree-house and walk down, so that you enter a secret back door into a small room. Following the ladder and the resultant underground cave trail (complete with random battles) leads you into the enclosed area with the Djinni, ready for grabbing.

Description
When Set, it increases base HP by 9, base Defense by 2, base Agility by 2, and base Luck by 1.

When Granite's battle effect is used, all currently active and alive Adepts are buffed for until the end of the turn with a protective effect that decreases all damage done to them from enemy attacks by 50%. This effect has the "strikes first" property, meaning it will be the first performed action in a given turn regardless of the agility rating of the user and any other unit in battle. Djinn with the same type of effect include the Mars Djinni Flash, which decreases damage done by 90%, and in The Lost Age the Mercury Djinni Shade, which decreases damage done by 60%.

Ability analysis
In Golden Sun, Granite is extremely useful from the moment it is collected all the way up to the end of the game, because of a very reliable damage-reduction effect. It is typically used in boss encounters, and can give your party a much needed cushion against enemy damage while other Adepts of your party focus on healing dangerously low-health party members. Much later in the game, the Mars Djinni Flash provides a much stronger version of the same effect, but even then Granite is not necessarily considered "obsoleted to uselessness", as both Djinn can be used and alternated between.

In The Lost Age, when Isaac's party joins Felix's party along with their returning Djinn, Granite tends to get more ignored because of the presence of Mercury Djinni Shade, which is essentially a slightly stronger Granite to better complement Flash. If the game is being played with the Adepts in their respective mono-elemental classes, then a Venus Adept using Granite essentially limits his "proper" role as a damage dealer, while Shade is somewhat of a better fit on Mercury Adepts, which are somewhat more oriented toward healing.

Name Origin
Granite is a type of igneous rock. Granite is almost always large, hard, and tough, so it is often used in construction. These characteristics may be why the Djinni Granite was given defensive abilities.