The Sapphire is a common gem found in caves which emits a small amount of dim light for a few blocks.
The Sapphire is used to craft:
-The Sapphire upgrade at the portal (1 Sapphire, 40 Time Crystals)
-Sapphire Pickaxe (5 Sapphires, 40 Time Crystals)
-Sapphire Chandeler (5 Glass, 10 Sapphires)
The Sapphire isn't a very rare gem and you can find easily it in a cave.They appear to be floating when first seen and can be mined as you would pick up an item, it will then make a loud chime noise. Sapphires can also be obtained using a Gold Pickaxe on rocks, such as Stone and Limestone.