Break your own geodes! Moroccan Quartz geodes. These have all been graded to have a high probability of being hollow & filled with crystals. There is still a chance that you will crack open your geode to find solid quartz instead of a cavern of crystals, but the fun is still in the opening of the geode & being the first to ever discover whats inside - hollow geode or not. The last photos show examples of what you might find inside.