It's nice to have variety in the game, so add Tin ore, which is stronger than stone and weaker than copper.

Thanks for your feedback! Variety is great. Right now, after stone, I have bronze (beach biome), iron (winter biome), and obsidian (grimwood biome) planned. I’m a bit worried that adding more ores per biome could lead to too many different factories, which might make things feel a bit overwhelming.