The diffusivity was measured under 0.1 to 200MPa at 600 to 800C in a pure CO2 atmosphere. The samples were single pre-annealed crystals of Chihuahuan calcite in an isotopically labelled atmosphere, and the diffusion profiles were measured using secondary ionization mass spectrometry. At 800C, The diffusion at 0.1MPa was described by:

D(cm2/s) = 0.62 exp[-291(kJ/mol)/RT]

The activation energy was nearly twice that (∼166kJ/mol) determined for 100MPa. A change in the slope of logD versus pressure, and the change in activation energy between 0.1 and 100MPa, suggested that the migrating C species changed from carbonate anions at low pressure to carbon atoms above 50MPa.

T.C.Labotka, D.R.Cole, L.R.Riciputi, M.Fayek: American Mineralogist, 2004, 89[5-6], 799-806