Manganese Dioxide Powder

Very fine, deep black powder that is used as a catalyst with hydrogen peroxide.  Dump a capful into a 2-liter pop bottle with 2 oz hydrogen peroxide, and the peroxide decomposes into oxygen and water.  Since this is an exothermic reaction, the watar turns to steam and rises mystically out of the bottle, while the bottle crinkles and melts due to the heat that is produced.

LL Demos & Labs:  Genie in a Bottle