This work is the first part of a study and deals mainly with issues related to heat treatment. The second part, which will present petrographic analysis and mechanical properties of cast stone, will be published separately and will be a direct continuation of the first part. The reader will find here a description of certain transformations occurring in specific temperature intervals, which the author has termed critical points and which have been discovered for the first time in materials made from molten rocks. A fairly detailed analysis of heating and cooling rates near the critical points is presented, allowing the author to draw a number of conclusions that have great practical significance and can introduce substantial changes into all technological processes of stone casting.