Ice9

Ice-nine is a fictional material conceived by writer Kurt Vonnegut in his novel Cat's Cradle. It is supposed to be a more stable polymorph of water than common ice (Ice Ih) which instead of melting at 0° Celsius (32° Fahrenheit), melts at 45.8°C (114.4°F). When ice-nine comes into contact with liquid water below 45.8°C (which is thus effectively supercooled), it acts as a seed crystal, and causes the solidification (freezing) of the entire body of water which quickly crystallizes as ice-nine. A global catastrophe involving freezing the Earth's oceans by simple contact with ice-nine is used as a plot device in Vonnegut's novel.

Vonnegut came across the idea while working at General Electric:

The author Vonnegut credits the invention of ice-nine to Irving Langmuir, who pioneered the study of thin films and interfaces. While working in the public relations office at General Electric, Vonnegut came across a story of how Langmuir, who won the 1932 Nobel Prize for his work at General Electric, was charged with the responsibility of entertaining the author H.G. Wells, who was visiting the company in the early 1930s. Langmuir is said to have come up with an idea about a form of solid water that was stable at room temperature in the hopes that Wells might be inspired to write a story about it. Apparently, Wells was not inspired and neither he nor Langmuir ever published anything about it. After Langmuir and Wells had died, Vonnegut decided to use the idea in his book Cat's Cradle.[1]
The fictional ice-nine should not be confused with the real-world ice polymorph Ice IX, which does not have these properties.