http://en.wikipedia.org/wiki/Cat's_Cradle

"As the novel progresses, the narrator learns of a substance called ice-nine, created by the late Hoenikker and now secretly in the possession of his children. Ice-nine is an alternative structure of water that is solid at room temperature. When a crystal of ice-nine is brought into contact with liquid water, it becomes a seed that 'teaches' the molecules of liquid water to arrange themselves into the solid form, ice-nine; this is similar to the actual process of freezing of normal water. However in the case of 'ice-nine' this process is not easily reversible, as the melting point of ice-nine is 114.4 degrees Fahrenheit (45.8 degrees Celsius)."

Needless to say, this stuff would be deadly if introduced into the environment, since all the water in the oceans would solidify and could only melt in the hottest places on earth. Ice-9 was also heavier than water, so the oceans would freeze from the bottom up. Nevertheless, the military is interested in Ice-9 as a material to solidify mud and snow to allow the passage of heavy vehicles. I used to think that this was too ridiculous a premise, even for a satirical science fiction novel ,until just a few years later I heard the military was studying the concept of pumping large amounts of phosphors into low earth orbit to absorb sunlight and produce artificial moonlight to help fight the Vietnam War.