Metastable:
In physics, metastability is a stable state of a dynamical system other than the system’s state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball is only slightly pushed, it will settle back into its hollow, but a stronger push may start the ball rolling down the slope. Bowling pins show similar metastability by either merely wobbling for a moment or tipping over completely. A common example of metastability in science is isomerisation. Higher energy isomers are long lived as they are prevented from rearranging to their preferred ground state by (possibly large) barriers in the potential energy. [Wikipedia]
Noted in “Bigger bang theory: teach atoms new tricks to beef up explosives,” David Hambling, NewScientist (29 July 2017, paywall):
A good way to change a game is to change its rules. One line of research to do just that builds on a curiosity that was exercising the Royal Society back in the 1660s just when gunpowder was: Prince Rupert’s drops. These tadpole-shaped trinkets are formed by molten glass cooling rapidly, and are named after Prince Rupert of the Rhine, a cousin of King Charles II who first brought them to England. The way the drops form leaves them under tremendous internal strain. A hammer will bounce off the drop’s body and not break it, but if you snap the tail the strain is suddenly released, sending a wave through the drop, shattering it into powder.
This explosivity is based on the release of not chemical energy, but mechanical strain. At the US Army Research Laboratory (ARL) in Maryland, Jennifer Ciezak-Jenkins and her colleagues have been experimenting with the same principle using nanoscopic diamonds. Diamond forms only at high temperatures and pressures, such as those found deep in Earth’s mantle, and is a “metastable” form of carbon. It is stable in ambient conditions, only crumbling over cosmic timescales back to graphite.
