mineralogical changes that occur during eogenesis are dependent on the environment in which that sediment has been deposited. for example, the formation of pyrite is characteristic of reducing conditions in marine environments. pyrite can form as cement, or replace organic materials, such as wood fragments. other important reactions include the formation of chlorite, glauconite, illite and iron oxide (if oxygenated pore water is present). the precipitation of potassium feldspar, quartz overgrowths, and carbonate cements also occurs under marine conditions. in non marine environments oxidizing conditions are almost always prevalent, meaning iron oxides are commonly produced along with kaolin group clay minerals. the precipitation of quartz and calcite cements may also occur in non marine conditions.