Dropped by the variant form of the blue slime king, the "Tentacle-Girl", Sapphire ore is on the same tier as Emerald ore in terms of strength and usability, but it's latent power is slightly different. It has the capability to access the water elemental, which is equally as effective against dragons and fire as the wind elemental is.
Unlike Emerald Ore, Sapphire ore is only meant for weaponry, and it cannot be fused into armor to strengthen it. Armor can be decorated by Sapphire ore, but no different properties would be applied other than a cosmetic difference.
Much like the Emerald ore, Sapphire ore-based weaponry has storage of energy for releasing the elemental, the more used at one time the longer it takes to recharge the capacity.
And just as with Emerald ore, Sapphire Ore has yet to be obtained in-game by any user, and as it's a completely new item, its general properties are currently unknown. These uses will become clearer as the open beta progresses