The Sapphire Ore is a block and resource added by Project Red. The block is added to the world by the world generation and the player can quarry the block with an Iron Pickaxe, or higher, to gain 1 to 3 Sapphires. With a pickaxe with silk touch, the player receives the block.
In the "ProjectRed.cfg" configuration file (in the "config" folder), the generation of Sapphire Ore can be disabled, and the generation can be reduced by increasing the resistance value.
Furtermore, the enabling of the retro generation allows to generate the ore in an old world, which was started with older versions or without Project Red.