Minecraft wiki entry for Mining, associated text: TNT mining is dangerous. If you must do it, you can use the 3-in method: First find a solid stone wall, mine 3 blocks inward, then place 1 block of TNT on the third hollowed out space. Once placed with flint and steel in hand, they right-click it with the flint and steel and back up a few steps and quickly block off the front of the hole with one block of stone. The explosion should create a perfect 3×3×3 hole. Repeat as desired.