Bismuth Geode/ bismuth that has been grown and cooled in an eggshell! Apparently bismuth is one of the easiest crystals to grow yourself. Bismuth does not naturally occur in geode form. What fun to create your own dragon's egg!
30 Eco-Chic Houses Made of 10 Types of Recycled Materials
Building with tires is good for the environment - but I'm not sure about the homeowners. As the tires slowly break down they're releasing chemicals into the home. If you build with tires be sure to seal them completely for at least a partial barrier of protection.