Does anyone have any sample of carbonate (Yellowstone travertine?) that is
particularly light in delta O-18, around zero on the SMOW scale, that they
would be willing to give me? It does not have to be especially well
characterised or clean, since I would be wanting to use it to equilibrate
with water and would characterise the gas myself. Something on the order
of 5g would be ideal (about 2 litres at atm pressure).