Dolomite samples were collected from four different locations of Salem, Tamil Nadu and the percentage of dolomite present in these samples were studied using Fourier Transform Infrared Spectroscopy (FT-IR). The thermal decomposition behavior of sample which has more percentage of dolomite has been studied by thermogravimetric (TG) and Differential Thermal Analysis (DTA). TG-DTA analyses provide two-stage thermal decomposition of dolomite. In the first stage, the formation of MgO and calcite was observed at around 750° C and in the second stage the decomposition of calcite at 890°C. The X-ray diffraction analysis (XRD) confirmed that the structural degradation of dolomite and formation of calcite at 700 °C. Scanning Electron Microscope (SEM) indicates that the disorderedness takes place at 700°C.