In mountain biomes, small patches of infested stone generate. They stand out a bit and you immediately know that they're infested.
To reproduce
Seed: -5783768960641278077
Coordinates: /execute in minecraft:overworld run tp @s 115.21 -28.80 41.21 -475.33 -11.55
Linked issues
is duplicated by 9
4 more links
from my knowledge(which is little) is removing infested stone from below grimstone level or adding infested grimstone that generate in grimstone levels.