We have analyzed elemental and mineralogic contents of 12 peat samples to better understand the factors controlling the nature and distribution of inorganic matter in peat. Peats were collected from a variety of depositional and ecological settings, including marsh environments in Florida and Georgia, raised bogs in Minnesota and Maine, various swamp-forest environments in Florida, Georgia, North Carolina, Minnesota, and New York, and an intertidal environment in southern Florida. Peat type was defined by petrographic analysis. Elemental contents of peats dried at 50 °C were determined using neutron activation; high-temperature ash (HTA) residues were analyzed using x-ray fluorescence. Mineralogies of low-temperature ash (LTA) residues were obtained using x-ray diffraction and scanning electron microscopy. HTA contents of the peat samples ranged from 0.38 to 30.65 wt %. Compositions of HTA residues showed a great range (e.g., Si, 3.5 to 42.5 wt %; Ca, 0.15 to 34.4 wt %; Mg, 0.17 to 20.3 wt %). Mineralogies of LTA residues also varied greatly. Quartz was present in all samples, generally as the dominant crystalline component. Corundum and bassanite, artifacts of the low-temperature ashing procedure, were present in 10 and 8 samples, respectively. Halite was abundant in the sample collected from the intertidal environment. Other minerals present in lesser amounts were alkali feldspar, muscovite, kaolinite, smectite, and pyrite. Poorly crystalline or amorphous material was present in all samples; in some it composed the majority of the LTA residues. The presence of poorly crystalline material made correlation between elemental and mineral contents difficult. Factors controlling the amount and type of inorganic material in these peats are: (1) underlying bedrock or sediments; (2) detrital source areas; and (3) the ecology of the peat-forming botanical communities. Our results show that it is unreliable to generalize peat inorganic contents based solely on geographic province or botanic communities.