Lansfordite is a mineral of magnesium carbonate (MgCO3). It represents the pentahydrate of magnesium carbonate, and has the total formula MgCO3·5H2O . Landsfordite was discovered in 1888 in a coal mine in Lansford, Pennsylvania. It crystallizes in the monoclinic system (space group P21/c) and typically occurs as colorless to white prismatic crystals and stalactitic masses. It is a soft mineral, Mohs hardness of 2.5, with a low specific gravity of 1.7. It is transparent to translucent with refractive indices of 1.46 to 1.51. The mineral will effloresce at room temperature, producing nesquehonite.