Obsidian

Obsidian is a very hard ore found in the volcanic biome. It is a late-game resource with a very narrow use case, making it easy to overlook unless you are specifically planning defensive infrastructure.

Its only known purpose is as an ingredient for crafting Combat Chipset, and Combat Chipset itself is only required when building an Electric Trap. Because of this chain of dependency, Obsidian is usually only needed in small amounts. Even if you intend to rely on Electric Trap for defense, mining just a few tiles is typically enough to cover your needs.

Since its role is so limited, Obsidian is best treated as a targeted mining resource rather than something to stockpile heavily. Once you have gathered enough for your planned traps, additional excavation is generally unnecessary unless you expect to expand that defense network later.