Oxygen is a blue crystalline solid at room temperature

Twenty-five years ago I went to a seminar with this intriguing title. The photographs of a deep blue substance trapped in a diamond vise were stunning, particularly in a time when black and white slides dominated the colloquium scene. Things get even more colorful if you explore the phase diagram of oxygen at higher pressures and temperatures (beyond 650 K and 16.7 GPa). A recent paper in Physical Review Letters (PRL 93, 265710, [2004], "New Phase Diagram of Oxygen at High Pressures and Temperatures", M. Santoro, E. Gregoryanz, Ho. Mao, and R. J. Hemley) revealed new solid forms of oxygen. The ε solid phase is a red crystalline form.

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What's a GPa? A gigapascal...or about 10,000 atmospheres.

Read early entrys about phase diagrams and literature.