Cobblestone

Cobblestone is a Block, obtained from mining Stone, Cobblestone, or from Cobblestone Minions.

Obtaining
Cobblestone can be obtained from mining Stone found in the Private Island (and 8 can be found in the starter chest), Coal Mine, Gold Mine, Deep Caverns, and all areas inside it. Mining Stone or Cobblestone grants +1 XP.

Cobblestone can also be bought from the Mine Merchant for each, or the Builder for  each.

The best way to actively collect Cobblestone on your private island is with a Stonk with Miner's Outfit set equipped and a Cobblestone generator. On public islands, it would be the same setup with Mineral Armor. For players who choose not to purchase or can not afford a Stonk, an Golden Pickaxe can be used with a  potion instead. Both options will allow the player to insta-mine cobblestone.

To obtain cobblestone collection 10 with only Cobblestone Minions, assuming you had 24 Tier 12 Cobblestone Minions, it would take around 583 minutes or about 10 hours to obtain 70,000 cobblestone not accounting for storage.

Collection
Collecting cobblestones increases the player's cobblestone collection, which grants useful items and perks upon collecting certain amounts of cobblestones.

Usage
Cobblestone can be used as a basic building block on the Player's Island. Cobblestone can be used to craft the Cobblestone Minion, and it can be crafted into Enchanted Cobblestone.

Cobblestone can either be smelted in a furnace, or mined with a pickaxe enchanted with Smelting Touch to get Stone.

Cobblestone can also be sold to any Merchant for per block.