Minecraft wiki entry for Safe_home, associated text: In the same manner that sand or gravel makes a poor choice for flooring or a foundation, obsidian is particularly good, due to its high explosion resistance. While it is unlikely that you will be able to produce enough obsidian to build entire walls or floors out of it, it can still be used for foundations, wall trim, and entrance frames. If you are indeed going to use a large amount of obsidian, you may wish to see Tutorials/Obsidian farming.