Instructions
Launch Minecraft and open up any previously-played world map. You can use any non-creative game mode.
Create four buckets by positioning iron ingots on a crafting table grid in a "v" pattern. Place one ingot in the left-center crafting square, one ingot in the center-bottom square, and a final iron ingot in the right-center square. Highlight the bucket icon and place it in your quickbar. Repeat this process to create four buckets.
Locate a non-moving or "source" lava block. Hold the bucket as your active block and press the left trigger on your Xbox controller to pick up the lava in your bucket.
Locate a non-moving or "source" water block. Press left trigger on your Xbox controller to pick up the water in your bucket. Repeat this process until you have three buckets of water.
Find a plot of dirt that is at least three blocks wide, five blocks long, and two blocks deep.
Dig two parallel trenches one block apart. Each trench must be five blocks long, one block wide, and two blocks deep.
Dig a deep center trench that is five blocks long, one block wide, and three blocks deep between the two trenches creating in the previous step. These three trenches should be parallel to each other.
Pick up any dirt blocks that have dropped from digging the trenches.
Place a row of dirt blocks just below ground level over the deep center trench.
Place a bucket of water at the each end of one of the outside trenches, then place the third bucket of water in the center of the same trench to create a standing water trench.
Place five redstone dust blocks at the bottom of the opposite outside trench to create a redstone trench.
Place the bucket of lava at either end of the redstone trench, just below ground level. This creates a source block of lava. Allow a few moments for the lava to spread from one end of the redstone trench to the other.
Use an empty bucket to pick up the source block of lava. Allow a few moments for the flowing lava blocks to disappear. The redstone transforms into obsidian blocks under the lava.
Use a diamond pickax to break and collect the obsidian blocks.
Place the redstone dust in the redstone trench, then place lava over it again to generate more obsidian blocks. Repeat until you collect the desired number of obsidian blocks.