Quartz

Location
Quartz is located late in Mogall Forest. In a screen you enter down from the top end, to the right of the screen is a rock right below a horizontal log - position yourself above the log and use Move to move the rock down one space into the circular indenture in the ground, then push the log down. Push a second horizontal log down, push the vertical log from the right to left, and go down and left to reach the Djinni. It must be battled to be acquired.

As an opponent
Statistically, Quartz has 349 HP, 25 PP, 127 Attack, 28 Defense, 76 Agility, and 9 Luck. Like all other Venus Djinn that are fought, in terms of resistance, it has a Venus Resistance rating of 193, Mercury and Mars Resistance ratings of 100 each, and a Jupiter Resistance rating of 25, and in regards to its abilities it uses its available Venus-based attacks with a Venus power rating of 125.

Quartz can use the following battle commands:
 * Earthquake: Used 53 out of 256 times, this is a Psynergy spell that prompts three rectangular sections of ground underneath the party to jolt upward and retract into the ground quickly twice in succession, bouncing each Adept twice. It dealing a Veus-based attack with a power rating of 35 and a range of 5. This ability consumes 7 of its user's PP.
 * Spire: Used 47 out of 256 times, this is a Psynergy spell that causes a thick stalactite to fall out of the sky and shatter onto a target, dealing a Venus-based attack with a power rating of 40. This ability consumes 5 of its user's PP.
 * Gaia: Used 41 out of 256 times, this is a Psynergy spell that causes the ground beneath the enemy to open up and engulf the party in a wide reverse shower of Venus energy and medium-sized boulders, dealing a Venus-based attack with a power rating of 40 and a range of 3. This ability consumes 7 of its user's PP.
 * Mad Growth: Used 35 out of 256 times, this is a Psynergy spell that causes a group of thorny vines to erupt from the ground and through the Adepts for a short time, dealing a Venus-based attack with a power rating of 60 and a range of 3. This ability consumes 10 of its user's PP.
 * Briar: Used 29 out of 256 times, this is a Psynergy spell that causes a series of quite large spiked vines to grow out of the ground quickly to assault the opposition, dealing a Venus-based attack with a power rating of 70 and a range of 3. This ability consumes 11 of its user's PP.
 * Attack: Used 28 out of 256 times, this is this monster's standard physical attack, but for this monster it is counted as a Venus-based attack rather than a non-elemental attack.
 * Flee: Used 23 out of 256 times, this enemy has the ability to attempt to Flee the battle, thereby ending the battle if successful without rewarding you with the associated EXP, Coins, and the Djinni itself, and the Venus Djinni disappears from its field spot. If this happens to you, you should walk back up out of the top of the screen and reenter, and re-solve your way to Quartz' position.

When defeated, Quartz yields 172 EXP and 201 Coins, and the Quartz Djinni is added to your party's Djinn collection. If you fell it with an offensive Jupiter Djinni like Gust, its rewards increase to 223 EXP and 261 Coins.

It is possible to have three Jupiter Djinn in your collection at this point, so having Ivan summon Procne with them will deal over 200 damage to Quartz in one blow - from this point onward, it becomes easy to defeat and earn Djinn because of the amount and power of summons you can unload in the beginning of a battle.

Description
When Set, it increases base HP by 10, base PP by 3, and base Agility by 3.

When Quartz' battle effect is used, a targeted downed party member has a 50% chance to be revived, with their HP restored to 50% of their maximum HP meter.

Ability analysis
Early in Golden Sun, Quartz can be potentially very useful as a means to try to get a downed Adept alive again if you don't have/want to use a Water of Life, even though that item is guaranteed to work and restores the Adept to 100% HP. Once the Revive Psynergy starts becoming available to Adepts at level 19, however, this Djinni's battle effect becomes immediately obsoleted, because Revive has the exact same properties of the Water of Life - guaranteed chance to revive at 100% HP, and may be used both outside and inside battle, for "only" 15 PP. Revive is a staple that is pretty much always used over not just Quartz, but its later superior counterpart, the Mercury Djinni Dew (which revives to 80% HP at an 80% chance).

In The Lost Age, when Isaac's party joins Felix's party along with their returning Djinn, Quartz's ability (and Dew's, for that matter) is all the more inferior as an in-battle reviving option because in addition to Revive being used as often as ever, there are other Djinn with better reviving effects, like the Mars Djinni Tinder that guarantees revival to 100% health, and the Mercury Djinni Balm which has a 60% chance to revive all downed Adepts in the currently battling party to 60% maximum HP each.

Name Origin
Quartz is a type of crystal commonly found in the Earth's crust.