Diagenesis refers to all those processes which occur to a sediment after deposition, during burial and any subsequent uplift. Sediments which undergo deep burial or are involved in orogenesis, such that they experience high pressures and/or temperatures, will undergo metamorphism and no longer be classed as sediments. There is no hard and fast boundary between diagenesis and metamorphism. As a guide, limestones will retain sufficient of their primary features that the depositional texture is still recognisable, whereas their metamorphosed equivalents will show little or no sign of the depositional fabric. However, this rule cannot be applied to dolomites where replacement under sedimentary conditions can lead to total obliteration of the original texture. Diagenesis certainly embraces processes that can occur at up to several kilometres of burial and temperatures well above 100ºC.