Dolomite sand has several contain such as CaCO₃ and MgO which have the potential as an antibacterial material. This sand is obtained from the Jedih Bangkalan hill, which has been utilized as a building material. Dolomite sand extraction can be done by calcination method with holding variation from 0.5 until 2.5 hours at 700 °C. Furthermore the powder from the calcination process was characterized by XRD to identify the phase. Goal of this research was to determine the effect of holding time on phase formation in dolomite. This result of XRD analysis exhibit as dolomite extraction has four phases namely calcite (CaCO₃), periclase (MgO), calcium hydroxide (Ca(OH)₂) and lime (CaO) with different percentages in each variation of holding time. Ca(OH)₂ and CaO phases denote of the impurity phase with a lower percentage than the CaCO₃ and MgO phase percentages. The most dominant phase is CaCO₃ and MgO phase formed optimally at one hour holding time with a percentage of 47.1% CaCO₃ and 35.9% MgO.