Obsidian Mining Cells can be found in Iron Treasure Chests on the Lava layer underground sometimes, or can be crafted in your Crafting Menu (default key "Q") or at Crafting Tables (that still exist in worlds created before R22 on September 16th 2015). However before being able to craft these Power Cells, it's necessary to unlock the crafting-recipe by crafting or taking a Stone Mining Cell. To craft one Obsidian Mining Cell, you'll need (as of R25 in November 2015): You will need the Obsidian Mining Cell to pull Siltstone, Stalactite, Saltrock and Glowing Mushrooms on the Stalactite layer.