Minecraft wiki entry for Nylium, associated text: Using bone meal on netherrack that is placed next to or adjacent to warped or crimson nylium transforms the netherrack into nylium of that type. No block can be above the netherrack during this process. This transformation can also be done by activating a dispenser with bone meal directly into that netherrack block. If both variants are present, there is an equal chance of either being spread.