The lattice parameters, cell volume, and structure of a sample of phase pure triclinic tricalcium silicate were determined using in situ, high-temperature synchrotron powder diffraction and full-profile Rietveld refinement. The temperature range covered was from ambient to 740degreesC. Evidence of superstructure was found. The T-2 type structure with disordered SiO4 tetrahedra was observed, and an average structure for the subcell (P (1) over bar, a = 11.7416(2) Angstrom, b = 14.2785(2) Angstrom, c = 13.7732(2) Angstrom, alpha = 105.129(1)degrees, beta = 94.415(1)degrees, and gamma = 89.889(1)degrees) is presented. Differential thermal analysis and X-ray fluorescence was also performed.