How to Make a Cobblestone Generator

Why build a cobblestone generator?

• Unlimited cobblestone without mining.
• Essential for skyblock and oneblock servers where stone is scarce.
• Can be scaled to produce thousands of blocks per hour when combined with pistons or TNT.
• Smelting cobblestone into stone or further into smooth stone provides XP and building material.

Materials list (basic design)

Step-by-step: Basic cobblestone generator

Step 1: Dig the channel

Dig a trench that is 1 block wide, 1 block deep, and 6 blocks long. This is where the water and lava will flow toward each other.

Step 2: Place the water source

Place a water bucket at one end of the trench. The water flows down the channel. It should stop flowing about 3 blocks in because of the trench length.

Step 3: Place the lava source

Place a lava bucket at the opposite end. Lava flows more slowly and has a shorter range. When the leading edge of the lava flow meets the water flow, cobblestone forms at that junction.

Top-down view:

  [WATER] ---flow---> [COBBLE] <---flow--- [LAVA]
  [BLOCK] [BLOCK] [BLOCK]  [BLOCK] [BLOCK] [BLOCK]

Step 4: Mine the cobblestone

Break the cobblestone block that formed. A new one appears immediately because the lava and water continue flowing into the same spot. You now have an infinite loop. Never mine the block directly adjacent to the lava source or you will release lava onto yourself.

Step-by-step: Piston-based automatic generator

Step 1: Build the generation chamber

Create a 1-wide channel with water on one side and lava on the other, just like the basic design. But this time, place a piston facing the cobblestone formation point.

Step 2: Add the piston and observer

Place an observer watching the block where cobblestone forms. When cobblestone appears, the observer sends a redstone pulse to the piston. The piston pushes the cobblestone out of the formation spot, making room for a new block to generate.

Step 3: Build a collection line

The piston pushes cobblestone into a line. After 12 pushes, the line is full (pistons can only push 12 blocks). Place a wall at the end and mine the row manually, or set up a second system to break the blocks.

Side view (piston design):

  [WATER]>[COBBLE FORMS HERE]<[LAVA]
            |
         [PISTON] ---> pushes cobble out
            |
         [OBSERVER] detects new block

Step-by-step: TNT-based mass generator

For large-scale production, use a TNT duper to break the cobblestone as fast as it generates. This produces thousands of blocks per hour as item drops, collected by water streams and hoppers.

Step 1: Build a lava-water formation grid

Create multiple cobblestone formation points in a row (8 to 16 points). Each point uses one lava and one water source, arranged so cobblestone forms in a line.

Step 2: Install the TNT duper above

A TNT duper positioned above the formation line detonates duplicated TNT. The explosions break the cobblestone row into dropped items. The items fall into water streams below, which funnel them into hoppers and chests.

Step 3: Time the cycle

Use a hopper clock or repeater chain to fire the TNT duper every 3 to 5 seconds. This gives the cobblestone enough time to regenerate before the next blast.

How cobblestone generation works

When flowing water meets flowing lava, the lava becomes cobblestone. When flowing water meets a lava source block, the lava source becomes obsidian. When flowing lava meets a water source block, the water source becomes cobblestone. The key is to use flowing lava meeting flowing water so that neither source is consumed. The trench design ensures both sources remain intact and only the meeting point becomes cobblestone.

Stone generators work differently. If flowing lava lands on top of a water source block (from above), stone forms instead of cobblestone. This is useful if you want stone directly without smelting.

Common mistakes

• Mining the wrong block. If you break the block adjacent to the lava source, lava flows out and burns you or destroys your water source. Always mine the cobblestone, never the blocks next to the lava.
• Water turning lava into obsidian. If water touches the lava source block directly, it converts to obsidian and your generator breaks. Keep a 1-block gap or wall between the water flow and the lava source.
• Piston line overflowing. Pistons push a maximum of 12 blocks. If you do not clear the line in time, the piston jams. Add a breaker or manual clearing schedule.
• Forgetting blast protection on TNT designs. Use obsidian or end stone for any walls near the TNT blast zone. Regular blocks get destroyed.

Efficiency comparison

Frequently asked questions

Can I make a stone generator instead?

Yes. If flowing lava drops onto a water source block from above, stone forms instead of cobblestone. This saves you the step of smelting cobblestone into stone. The layout requires a vertical lava flow meeting a horizontal water source.

Does this work on Bedrock Edition?

The basic and piston designs work on both Java and Bedrock. TNT duplication mechanics differ between editions, so verify your duper design matches your platform.

How do I prevent lava from burning dropped items?

In TNT designs, use water streams below the blast zone to catch items immediately. Items that land in water cannot burn. Alternatively, place the lava sources behind non-flammable walls so dropped items never contact lava.

Is this useful on survival servers?

Absolutely. Cobblestone is used for building walls, smelting into stone for decorative builds, and crafting stone tools, levers, buttons, and furnaces. On economy servers, selling cobblestone or smooth stone can be a steady income source.