Lesion Block

Placed anywhere in a normal world this block sits there inert. You can build an entire diseased-looking wing onto your base, run it right up against your herb garden, and nothing converts. That is the whole point of it, because Ebonstone would eat the garden.

The exception is the alternate world seeds, where the block generates on its own up in the sky and does count toward forming a corrupt biome. If you are building in one of those worlds, watch how much of it you pile into one room before something starts spreading.