The process of diagenesis excludes surface alteration (weathering) and metamorphism. Kerogen is formed during sedimentary diagenesis from the degradation of living matter. Minerals in a sedimentary rock can have formed by precipitation during sedimentation or by diagenesis. Oxidizing conditions are common in some environments of deposition and diagenesis of sedimentary rocks. Cementation occurs as part of the diagenesis or lithification of sediments. Older sediments are also more prone to corruption by diagenesis. Other deposits include recently deposited alluvium that has yet to undergo diagenesis. Most organics become kerogen by the end of diagenesis. The process of diagenesis is also important in the decomposition of bone tissue. Usually diagenesis results in a weak bedding-plane foliation. The term diagenesis, literally meaning "across generation", is extensively used in geology. Porosities can be very high when preserved from diagenesis by early hydrocarbon charge. The collapse can occur during diagenesis and dolomitization. This chemical change is an expression of diagenesis. Eogenesis refers to the early stages of diagenesis.