So much for "diamonds are forever." Scientists at Sandia National Laboratories have taken diamond, the hardest known natural material on Earth, and melted it into a puddle.

Diamond isn't easy to melt, which is why the scientists used Sandia's Z machine, the world's largest X-ray generator, to subject tiny squares of diamond, only a few nanometers thick, to pressures more than 10 million times the atmosphere's pressure at sea level.

"It's very difficult to reach those pressures," said Marcus Knudson, a Sandia experimenter.

To create the pressure, the machine's magnetic fields hurled small plates at the diamond at 34 kilometers per second (21 miles per second), or faster than the Earth orbits the Sun.

Researchers were investigating how the diamond reacted to a range of extreme pressures to see if it could be used to encase BB-sized fuel pellets needed to drive a nuclear fusion reaction.

Nuclear fusion occurs when multiple nuclei combine to make one heavier nucleus. If lighter elements are used, the reaction can create tremendous amounts of energy, but scientists are still learning how to manipulate and control fusion. (All current nuclear reactors harness the energy from fission reactions, where an atom splits into two or more smaller nuclei.)

To get a controlled fusion reaction, whatever material is surrounding the pellet must transmit any pressure applied evenly to the fuel inside to force it to implode. To do this, the material must either stay a solid or melt to a liquid--a mixture would create instabilities that could fail to compress the material enough and therefore "kill" the implosion, Knudson told LiveScience.

Currently, beryllium is being used to encase the pellets, but diamond is being considered as an alternate material because of problems with the beryllium leaking.