Calcium aluminates have a decisive influence on the hydraulic activity of cement, in this regard, detailed study of them is an urgent task. The aim of this study is to determine the phase composition and detailed analysis of the structural-phase state of monoaluminate calcium by X-ray analysis. To research monoaluminate calcium powder diffractometer DRON4-07 was used, it has been modified to a digital signal processing. Shooting was performed on the copper radiation (Kα) scheme Bragg – Brentano 0,020 increments and the exposure time at 1 sec, the angular range 6–82 °. The paper shows that the main phase in the mineral calcium is monoaluminate compound Al2O3. Also the following structural-phase states are identified: a structural motif AlCaO and connections Al2O3, Fe3O4, CaO. AlCaO structural motif is found in the form of two modifications (cubic and orthorhombic) with a high proportion of their total intensities (18.3 and 29.6 %, respectively). Also in the testing mineral the contribution in integrated intensity was found. The range of contribution was from crystalline and amorphous structures, in addition background radiation was also found. Reservation of short-range order in the arrangement of atoms is a specific feature of amorphous structures.