In order to study the thermal property of siderite (FeCO3) further, high purity siderite (FeCO3) was artificially synthesized by a simple solid reaction under high temperature and high pressure. The properties of the assynthesized siderite were investigated by X-ray powder diffraction and Raman spectroscopy, respectively. To find out the siderite stability region of a Pressure-Temperature (P-T) phase diagram, a high pressure synthesis was performed at various conditions, and in this case the principle of siderite synthesized under high pressure was strictly interpreted. The size of microparticles observed from Scanning Electron Microscope (SEM) image exceeds to 20 micrometers and the Fe content was quantified by Electron Probing analysis. As a typical and important Fe-bearing carbonate mineral, its thermal property is investigated by Thermogravimetric (TG) analysis and high temperature powder XRD refinement, and the thermal expansion coefficient along c-axis (alpha(c) = 7.995 x 10(-6) /degrees C), the thermal expansion coefficient along the a-axis (alpha(a) = 3.313 x 10(-6) /degrees C) and the volumetric thermal expansion coefficient (alpha(V) = 1.47 x 10(-5) /degrees C) was calculated.