Ore Nodes
From Subsistence Wiki
Surface / Rocky areas
Copper, iron, potassium, and zinc ore can be found overground (or rarely also in shallow water) as ore nodes on large rocks. The same is true for lithium, obsidian, and silicon ore, but those are notoriously less common and occur somewhat reliably only in a few regions respectively.
Underwater
Sandstone can only be found underwater in ponds and lakes.
Coal, Crystal, and Phosphate are significantly more difficult to obtain and occur only in the hazardous and hard-to-access underwater caves.
Finally, Black Crystal is exclusively found in the downright lethal subterranean lava caves.