In this study, microbial precipitation of carbonate was observed using high microbial urease activity, and it was found that the ratio of Mg/Ca affected the types of crystals produced. Without Mg²⁺, calcite was produced using only CaCl₂, while the presence of Mg produced Mg-calcite, magnesite and/or possibly dolomite of round, spherical or fibrous shapes, depending on reaction time, pH and Mg/Ca ratio. The carbonate produced contributed to the development of cementation for sands. The presence of Mg showed a relatively strong cementation of the carbonate.