These are rare drops from most trash mobs and guaranteed drop from some bosses in Molten Core.
As an ingredient
Lava Core is used in the following recipes:
As a quest objective
Lava Core is needed for the following quests:
- Patch 9.0.1 (2020-10-13): Item level modified due to level squish, from 60 to 25.
- Patch 6.0.2 (2014-10-14): Stacks to 200, up from 10.