Stormsoul Crystal
雷鬼晶 [raiki shou] or 'thunder oni crystal' in Japanese. Oni in this instance can mean either a Japanese-style demon or the spirit of a dead person.
Grimoire of the Rift

Buy: - (sell: 3,000 gil)
Use: Magick Hands, Judicer's Coat, Gaius Caligae
Reward: Sky Pirate Vaan x2 (once), Graszton Nightwatch (once), Unplumbed Depths (once)
Type: Magicite, Rank: ★★★
Description: Legend says that a great spirit of the storm lies trapped inside this crystal. Violent flashes of lightning arc through its depths.
Final Fantasy Tactics S

Buy: - (sell: 500 gil)
Use: ?
Obtain: Nation of Magic Nensa-Ramoi/Desert of Lightning lv60+
Description: A very uncommon piece of magicite
Category: Item