Hello everyone!
I had this idea in my mind when i started making this game, that player would not have easy access to all resources to force trading a little more, but it was not clear enough :D
Some of you did not know how to go further so in version 1.0.6 i added both clay and iron resources that can be mineable by workers.
These resources are limited like stones, can be healed and can still be traded. Coal and gold might be added in next version.
Thanks all and have fun :)