The invention relates to a particularly energy efficient, two-step method and to a system for the continuous or semicontinuous production of crystalline calcium carbonate (precipitated calcium carbonate, PCC) by reacting calcium hydroxide with CO2, the calcium hydroxide being lime milk. In the first step of the germination, the CO2-source is exclusively flue gas having a CO2-content of between 4-25% . In the second step, the complete conversion of the lime milk reacted in the first step to a maximum of 90%, preferably between 10-90%, is carried out exclusively using a rich gas which comprises 30-99% CO2, preferably using biogas.