An investigation of the behavior of excluded siderite samples derived from both pure mineral species and by density separation of pulverized coal samples was conducted at combustion temperatures of 1100 and 1600 degrees C. Analysis of quenched combustion residues collected from the combustion gases under oxidizing conditions was obtained via scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and X-ray fluorescence (XRF) spectroscopy. The FeO-MgO-CaO ternary phase diagram was used to predict the behavior of excluded siderite grains under combustion conditions and indicated that the siderite is unlikely to form sticky or completely melted particles at 1600 degrees C unless MgO < 5wt %, CaO < 37.5 wt % and (MnO + FeOn) > 60wt %. The extent of melting observed for collected particles having different compositions agreed with this prediction. By comparison with published work for excluded pyrite particles, residues from excluded siderite particles are found to be sticky at higher temperatures (1380 degrees C compared to similar to 1080 degrees C for pyrite), and will generate less fines as fume or by fragmentation. Slagging indices based on iron in ash for coals containing pyrite will therefore not apply to coals containing siderite.