Bacillus subtilis, a bacterium useful in some biotechnology applications, contains enzymes such as amylases, which play an important role in several industrial processes. One of its properties, not very well studied, is its capacity to induce the chemical bioprecipitation of CaCO3 (Ca 2+ + HCO 3 CaCO3 +H + ), a similar mechanism commonly observed in the formation of rocks, soils and biological structures like bones, shells and teeth. In this work we have studied carbonate crystals produced by a B. subtilis isolate collected from a gold mine in Segovia (Antioquia, Colombia). Its calcification capability was assessed by determining the production of CaCO3 crystals using the specific B4 media culture. In addition, mineralogical analyses were conducted, using techniques such as a binocular stereoscopy, plane polarized light optical microscopy (PPLOM), scanning electronic microscopy with energy dispersive X-ray detector (ESEM/EDX) and Fourier Transform Infrared spectroscopy (FTIR). These analyses showed that the native isolated strain of B. subtilis produces calcium carbonate (CaCO3) in its low temperature polymorphic form, (calcite).