gem mine

You can create a gem mine like the gold mine, so is too easy to make gems

Ruled out, read the stickies.

Supercell would lose income if they added this.

This is ruled out, read the stickies next time, but its a good idea anyway. Supercell wont add this because they will lose profit. Even it was extremely slow.

Gems should be left as a perk!
If you could mine them I'm sure it would lead to so many uneven and rushed bases!