We put together a few videos and a lot of info below to explain the process of chemical conversion calcium carbonate calcium oxide. This process is more commonly known as firing of limestone to create quicklime. Quicklime as many know is the key active ingredient in historic lime mortar.
Doing a little backyard chemistry, we burnt limestone to create quicklime. This is an extremely small batch process just done for the purpose of learning the chemical process. In real production masons most often create a comparatively massive batch of quicklime.
The videos below has a detailed description of the burning and associated chemical conversion process through burning with the addition of h2o.