Magnesium oxalate is an organic compound comprising a magnesium cation with a 2+ charge bonded to an oxalate anion.  It has the chemical formula MgCO.  Magnesium oxalate is a white solid that comes in two forms: an anhydrous form and a dihydrate form where two water molecules are complexed with the structure.  Both forms are practically insoluble in water and are insoluble in organic solutions.