Magic sand is ordinary sand that has been coated with trimethylsilanol, a compound that makes it resistant to water. The result is a hydrophobic sand that can be used in all sorts of interesting ways. This substance was originally developed for use in the cleanup of oil spills, but it has come to be used as a children's toy and educational tool instead. Many stores that sell science-orientated kid's toys stock it.
Because this sand resists water, it performs very strangely when exposed to it. The individual grains tend to stick together in the water, creating blocks that can be molded into various shapes. When scattered lightly across the surface of water, the sand will stick together and form a thin layer that will eventually get too heavy to float, sinking slowly to the bottom. This sand also appears slightly silvery underwater, thanks to the bubble of air that forms around the granules.
When lifted out of the water, the sand is perfectly dry and free-flowing. People who grew up playing with this product may remember how mesmerizing the mysterious substance was, as the seemingly solid underwater shapes would dissolve instantly when pulled out.
The idea behind this sand when it was initially developed was that it could be scattered across an oil spill to bond to the oil. As it did so, it would grow extremely heavy, eventually sinking to the bottom of the ocean and taking the oil with it. Magic sand proved expensive to manufacture, however, and doubts were raised about the environmental soundness of this cleanup method.
As a result of its commercial failure, the manufacturer was left wondering what to do with its new invention. The solution was to dye the sand in eye-catching colors, label it “magic sand,” “Mars sand,” or “space sand,” and sell it as a toy. This product was immensely popular in the 1980s, much to the chagrin of parents who had to clean up after their children, and it continues to be used in scientific demonstrations of the properties of hydrophobic materials.
Magic sand can be made at home by baking sand to remove the moisture and then coating it with a water repellent spray designed to protect fabric, tossing the sand to ensure that it is evenly coated.