The Mammoth Tusk (also known as Flint Edge in the SNES/PS version) is Crono's seventh-level weapon. It has an attack power of 40. You can trade for it at Ioka Village Hut for 3 Fangs and 3 Horns.
Contrary to its name, the weapon's sprite is colored with metal-white (the same color as the Bronze Blade and Empyrean Blade), though its slashing trail is that of a straight-lined yellow-orange flash with an impact effect in the slashing direction.