How much Oxygen is in ζ-phase metallic Oxygen? I am playing with a sci-fi idea of Oxygen storage for breathing. I wonder how do some compressed forms of Oxygen compare to human-breath-Oxygen (room temperature, room pressure) in terms of density.
Then, I've read a wikipedia article about solid Oxygen and it seems to explain that ζ-phase Oxygen is pretty high up on the density scale:
https://en.wikipedia.org/wiki/Solid_oxygen.
I hopelessly tried to convert 23.5 cm3/mol to a density measurement that I know (grams per cubic meter).
Also, I hopelessly tried to apply 96 GPa-pressurized Oxygen measurement to a density measure.
I am not a thermodynamics person :(
Will appreciate some extreme-density-Oxygen facts that I can play with :)
 A: One mole of oxygen is 32 grams. So the figure you cite tells you that 23.5 cm$^3$ of solid oxygen weighs 32 grams making the density about 1.36 g/cm$^3$ or 1360 kg/m$^3$.
For comparison the density of air is about 1.225 kg/m$^3$ and only 23% (by weight) of the air is oxygen. So the density of the oxygen in air is around 0.28 kg/m$^3$, which is a factor of nearly 5000 less than the solid oxygen.
A: BP  = 101.325 kPa
STP = 101.325 kPa,  0°C
NTP = 101.325 kPa, 20°C

Molar mass of oxygen = 31.9988 g                    [1]

Molar volume of gaseous  oxygen at STP = 22.41 L    [5]
Molar volume of liquid   oxygen at BP  = 28.04 cm³   -
Molar volume of metallic oxygen        = 23.5  cm³  [4]

Density of gaseous  oxygen at STP = 1,429  g/m³     [2]
Density of gaseous  oxygen at NTP = 1,331  g/m³     [6]
Density of liquid   oxygen at BP  = 1,141 kg/m³     [2]
Density of metallic oxygen        = 1,362 kg/m³  (calculated)

Ratio gas(STP):liquid:metallic = 1:798:953       (calculated)
Ratio gas(NTP):liquid:metallic = 1:857:1023      (calculated)

Note: Wiki [3] gives the gas:liquid O₂ compression ratio 1:861
      - it is likely at different conditions than at NTP or STP
      (possibly at around 25°C and BP)

Refrences: 
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[1] http://webqc.org/molecular-weight-of-O2.html
[2] http://en.wikipedia.org/wiki/Oxygen
[3] http://en.wikipedia.org/wiki/Liquid_oxygen
[4] http://en.wikipedia.org/wiki/Solid_oxygen
[5] http://en.wikipedia.org/wiki/Molar_volume
[6] http://engineeringtoolbox.com/gas-density-d_158.html

