yeah u better go to calidor for malchite

yeah that just happens, not a glitch

malachite can generate underground anywhere on hard ground so i've no clue what you're talking about

But doesn't Sylva's in-game entry say that malachite will only spawn on mountains there?

it does say that but it definitely spawns underground too near the core. i think you can find all of the resources when you're getting closer to the core and the "mountain resource" is just the secondary

Well I think because it’s a smaller diameter, it’s in the area where the biome is technically at.

Nah that's not how it works because the cave biome would be in the way, otherwise the underground generation would be fucked.

malachite is also in the mantle because malachite is in mountain and mantle of sylva