Dunlop, Ö. Özdemir, in Treatise on Geophysics (Second Edition), 2015. Iron Carbonates. The most common iron carbonate is siderite (FeCO 3), a frequent constituent of carbonate sediments and rocks on has a lowtemperature transition at 30–35 K (Housen et al., 1996), distinctively different from that of pyrrhotite (Section ).