Understanding the precipitation thermodynamics and kinetics of minerals is important for predicting and handling of separation and scaling of mineral depositions during gas processing. Calcium carbonate is one of the most abundant minerals precipitating in such processes and this work is focused on the precipitation of CaCO3 in presence of Monoethylene glycol (MEG) used as hydrate inhibitor during gas production. MEG is already known to affect the thermodynamics of calcium carbonate and this work shows that MEG also has a large impact of the precipitation kinetics. The whole precipitation process has been investigated and both the polymorphism induction times nucleation rates and growth rates have shown to be influenced by such co-solvent. The investigation is emphasised on the growth rates as these have a large impact on both the induction time measurements and the transformation rates. The investigation of the initial polymorphism revealed a promotion of vaterite at high concentrations of MEG and this polymorph is used as the model system when developing a method for growth rate measurements. The growth rates are reduced for all the polymorphs in presence of MEG both at conditions of gas processing where the ratio between initial calcium and carbonate can be large and at stoichiometric conditions. The slow growth of calcite in high MEG concentrations result in a very slow transformation from initially mixed metastable polymorphs. The decreased growth rate also prolongs the induction periods which is frequently used to determine nucleation rates. When the impact on the growth rate was taken account for in the determination of nucleation rates the nucleation rates were found to decrease with increasing MEG concentrations.