Stone is the second layer of the mine which is under dirt. You require 100 blocks mined to unlock this layer. It has twice the value of dirt.

Description: Edit

Dave's Ingame description: Stone, it's pretty hard. Used for building structures. Found around -170 blocks deep.

Ores: Copper, Silver, Gold, Ruby, Sapphire, Diamond, Emerald, Uranium, Turquoise, Amethyst, Platinum, Tektite and Adurite.