Glowstone blob

Glowstone clusters generate on the underside of terrain blocks in the Nether.

Info
These are typically veins of glowstone that can be among the hardest natural materials to harvest that don't require digging. They form in coral-like structures on the underside of hanging Netherrack, so they are often found on the ceilings of the Nether, where they provide light along with the ever-present lava.