2. Solid-phase equilibria

The ice diagram outlined by Bridgman is extremely rich: in 2005, in addition to the three amorphous forms of ice (known as low, high and very high density), fifteen crystalline varieties of ice were listed, numbered from I to XIV, with I ice itself comprising two varieties: stable Ih (hexagonal) ice and metastable Ic (cubic) ice. All snow and ice found naturally on earth is Ih ice. The varieties recognized as metastable are Ic, IV, IX and XII. Ice Ic can be obtained by condensation of water vapor below – 80°C; ice IV and XII result from slow heating (< 15 K/min for ice IV) or rapid heating (> 15 K/min for ice XII) of the amorphous high-density form, from 145 to 250 K under a pressure of...