Sample rietveld refinements of powder patterns exhibiting vaterite and calcite peaks. The red curves show the fit, the grey curves show the difference curve and the markers indicate the positions of the individual vaterite (blue) and calcite (green) peaks. a) Initial sample exhibiting vaterite features in sapphire capillary. The sapphire capillary exhibits a strong peak at 19.97° 2θ which has been removed from the plot. b) Powder pattern exhibiting vaterite peaks at a CO₂ pressure of 30 bar in quartz capillary.