The ammoniated magnesium chloride hexammoniate compound (HEX) is the key precursor phase required for the production of anhydrous magnesium chloride by the Australian Magnesium (AM) process. It is produced by direct ammoniation of MgCl2-saturated ethylene glycol solutions at 323 K. To determine the conditions required to form HEX, the C2H4[OH](2)-rich part of the MgCl2-NH3-C2H4[OH](2) system was investigated at 323 +/- 0.5 K. Seven phase regions were determined. These were: NH3(g)+Liq(T), HEX+Liq(T)+NH3(g), HEX +Liq(T), HEX-FT+Liq(T), T+Liq(T), MgCl2 center dot 3EG-FT+Liq(T), and Liq(T). The symbol T represents a ternary compound of composition MgCl2 center dot 2NH(3)center dot 2C(2)H(4)[OH](2), and Liq(T) represents a ternary liquid phase. To produce only hexammoniate in the AM process, bulk ammonia levels need to be maintained at levels of greater than about (11 to 13) % (w/w) NH3. At lower ammonia levels, the formation of T-phase is promoted, resulting in coprecipitation of HEX and T-phase.