The kinetics of formation of crystal boron was studied by X-ray structure and differential-thermal analyses. The enthalpy of transition of amorphous boron to crystal boron with formation of an intermediate non-equilibrium phase was determined by the calorimetric method. Studies were carried out by using the differential scanning calorimeter SETARAM. Amorphous boron received by diboron cracking was used as the starting material. The test sample is cha- racterized by stability even at a high temperature. When heated, amorphous boron first transforms to crystal boron of α-modification, and during a further heating, there occur several phase transitions, which means the transition of α-rhombohedric crystal boron to the β' and β'' metastable states. Studies of various modifications were carried out by radiographic and electro-optic methods. The high sensitiveness of the calorimeter made it possible to control temperature in the oven, make records and detect even the smallest thermal effects.