The J block is a block that looks like a face, and there is only one per survival map. It is always found where there is stone.
When shift-clicked, it tells the player its name and purpose.
How to Find the J Block
The J Block can also be found in all seeds once explored, but only in survival.
Hi. I'm J. I'm quite useless. For now.
This is what he says when you shift click on him. A red screen will also appear.