万年亀の甲羅 [mannengame no koura] or 'eternal turtle's shell' in Japanese.
Final Fantasy XII
Buy: - (sell: 1,337 gil)
Use: Venetian Shield
Drop: Adamantitan
Steal: Darksteel, Pandaemonium
Poach: Silicon Tortoise
Description: This shell is faded in color, but of remarkable durability and quality. These are prized by artificers for use in all manner of crafts.
Revenant Wings
Buy: 600 gil (sell: 300 gil)
Shop: Material Shop, chapter 6 onwards with over 100 materials obtained
Use: Ice Brand, Mythril Lance, Mythril Staff, Rod of Ice, Trident
Obtain: Maleficent Mayhem (harvest 11%), Baubles and Banditry (reward 25% with Goblin Pouch), The Trodden Past (treasure), Gucuma Qul Sky Pirate Melee (reward 25% with Goblin Pouch, harvest 11%), Fane of Tehp Qul Summoning Melee (harvest 11%)
Description: Carapace celebrated by engineers. Remains hard after luster fades
Other: high-grade Timeworn Carapace
Grimoire of the Rift

Buy: - (sell: 2,000 gil)
Use: Genji Shield, Lotus Mace, Rocket Punch, Shield of the Four
Reward: Hors d'Oeuvre of the Hour x4 (once), Caravan Cry x2 (once)
Type: Bone, Rank: ★★★
Description: This shell is only harvested when properly aged. A favorite material among certain craftsmen.
Final Fantasy Tactics S

Buy: - (sell: 200 gil)
Use: ?
Obtain: Federation of Nazan/Path of Fangs and Knives lv30+
Description: An uncommon bone
Category: Item