In an effort to increase sample density and maintain oxygen-free conditions, similar experiments were conducted at beamline X7B of the NSLS using the reaction cell shown in Fig. 2. For this study, an ex situ prepared anoxic slurry was heated to 1208C over 30 min and held for 3.5 h. During this time, mackinawite is the only Fe`S phase observed Fig. 4.. A trace amount of goethite was noted and is likely the result of a reaction at the slurryrcompressed N2 interface due to impurities in the reagent grade overpressure gas or in surface contamination during cell loading and mounting.