Bloodstone is a gem found in the Nether and the Voidwarp Nether.
Ores of Bloodstone are distributed ambiently throughout pockets of Netherrack in the Nether and Voidwarp Nether. They can generate at any height in pockets of 1-6 ores.
When mined, there is a 10% chance for ores to spawn a Bloodstone Golem. As these are small and strong, they pose considerable threat when mining Bloodstone. If one is speedy, they can be avoided fairly easily though.