Whole-rock and mineralogical composition of Phanerozoic ooidal ironstones: Comparison and differentiation of types and subtypes

Additional constituents of all the ironstones types are detrital quartz grains, apatite, organic material, pyrite (mainly framboidal) and calcite. Quartz grains may be absent, but may also occur in high quantities leading to ironstones with and without detrital quartz grains. Ironstones with high quantities of quartz grains resemble ooid-bearing sandstones. Apatite does not occur in the form of visible grains, but whole-rock analyses generally show that there is a distinct correlation between the CaO and P2O5, indicating the occurrence of apatite. Some ironstones may also be enriched in CaCO3 either in the form of detrital shelly material or as the youngest mineral in the form of calcite replacing many of the pre-existing minerals.