From Blocks to Bowser: The Super Mario Bros. Movie Phenomenon.
The director of the Super Mario Bros. movie, Aaron Horvath, has explained how the brick blocks float in the Mushroom Kingdom. He revealed that there is a mineral called "Floatanium" that is natural to the Mushroom Kingdom, which the Toads mine and transform into blocks for construction purposes. Although it never made it into the final movie script, it's a neat explanation for a long-standing question. The Variety feature also contains insights from Shigeru Miyamoto, Illumination CEO Chris Meledandri, and the film's cast.