How to make a cobblestone generator in Minecraft

A cobblestone generator gives you endless Cobblestone from one Lava Bucket and one Water Bucket. This version keeps the water away from the lava source, so it never turns into Obsidian. We built it on a Java Edition 26.3 server and timed it: every block came back 29 to 31 game ticks after being mined.

1. Dig a trench 5 blocks long, 1 block wide and 1 block deep, with solid blocks on both sides and at both ends (layer 3 of the plan).
2. In the fourth block of the trench, dig one block deeper: a 1 by 1 hole (layer 2).
3. Keep a solid floor under the rest of the trench. About 20 blocks of any kind are enough for the whole frame.

Pour the Lava Bucket into the first block of the trench, at the end away from the hole. Lava spreads 3 blocks from its source in the Overworld, toward the hole.

Pour the Water Bucket into the fifth block, right next to the hole. The water spills into the hole. Water that can flow down does not spread sideways, so it stays there and never reaches the lava source.

Where the flowing lava touches the water, it turns into Cobblestone: in the third block of the trench, between the lava and the hole.

Mine the block in the third position from above, or open the wall next to it, with any pickaxe. Lava only moves every 30 game ticks in the Overworld, so the next block forms 1.5 seconds later: up to 40 blocks a minute. A faster pickaxe does not help beyond that; Unbreaking and Mending keep it going for longer.

Cover the lava source with a block if you mine from the top, so you cannot fall into it.

Lava	Touches	Becomes
Flowing lava	Water, from the side	Cobblestone
Lava source	Water	Obsidian
Lava flowing down	Water below it	Stone
Lava over Soul Soil	Blue Ice next to it	Basalt

That is why the gap matters: if water ever touches the source block, you get one Obsidian and the generator stops.

We built and timed this generator on Java Edition 26.3. Lava and water make Cobblestone the same way on Bedrock Edition, but we have not timed it there.