>>51489070Ground is just that the ground, soil, and digging
Rock is about minerals and hardness
There is obviously going to be some overlap due to rocks being found in the ground but they are distinct concepts.
Diglett digs but it’s not rocky so it’s only ground
The Gen 1 fossil mons either had rocky bodies before extinct or became mineralized during fossilization, so they are rock, and get their second type due to where they lived while alive (water for the invertebrates and flying for the pterosaur).
If anything Steel has more in common than Rock than Ground does since Steel also represents hardness, but with a focus on metal and includes theme of technology.
If Pokémon only had 4 elements all three would likely be condensed into Earth.
