Where do silverfish blocks spawn in minecraft?

I'm in a survival world with a lot of mountains which makes me nervous because I'm not sure which biome silverfish blocks spawn.

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2 Answers

Blocks infested with silverfish only spawn in the extreme hills. They do not spawn naturally in the strongholds, this may be a misconception because silverfish spawned via the spawner may go into a block, which means they can be found there.

Infested Stone (Stone containing silverfish) spawn in extreme mountain biomes.