The ice found in our freezers—and, in fact, almost all the ice on planet Earth—is known to chemists as Ice I or Ih. The letter h signifies its molecules are arranged in six-sided hexagons. This is the only form of ice any of us are ever likely to run into. But it’s not the only one.
With changes in temperature and pressure, solids transform into different versions of the same substance. Their molecules stay the same but get arranged or stacked together differently. These alternative crystalline structures are called . Most
