SEDIMENTARY ROCKS/Mineralogy and Classification 25 SEDIMENTARY ROCKS Contents Mineralogy and Classification Banded Iron Formations Chalk Chert Clays and Their Diagenesis Deep Ocean Pelagic Oozes Dolomites Evaporites Ironstones Limestones Oceanic Manganese Deposits Phosphates Rudaceous Rocks Sandstones, Diagenesis and Porosity Evolution Mineralogy and Classification R C Selley, Imperial College London, London, UK ß 2005, Elsevier Ltd All Rights Reserved Introduction Rocks and Their Classification defined the three main classes of rock: igneous, metamorphic, and sedimentary It described the main features by which the three types of rock may be distinguished, and presented anomalous examples of each The classification of igneous and metamorphic rocks is described in Igneous Processes and Metamorphic Rocks: Classification, Nomenclature and Formation, respectively This article describes the mineralogy and classification of sedimentary rocks Sedimentary rocks are formed from the detritus of pre-existing rocks: igneous, metamorphic, or sedimentary The way in which rock is weathered, eroded, transported, and deposited is discussed in detail elsewhere (see Weathering, Sedimentary Processes: Fluxes and Budgets, Unidirectional Aqueous Flow, and Sedimentary Environments: Depositional Systems and Facies) Sediments possess a wide range of particle size, ranging from boulders to clay, and of chemical composition, including silica, lime, or ferromagnesian volcanic detritus These parameters of particle size and composition are used to classify sedimentary rocks Sedimentary rocks commonly exhibit two properties that may be used to differentiate them from igneous and metamorphic rocks Where they crop out at the surface of the Earth, sedimentary rocks generally show stratification (layering) The strata indicate successive episodes of deposition Layering is usually absent from igneous rocks, but is found in some metamorphic rocks When examined under the microscope, sedimentary rocks are generally seen to consist of particles Void space (porosity) is commonly present between the constituent grains Interconnected pores give the rock permeability Permeability allows fluids to migrate through rock, and enables rock and soil to drain Additionally, fossils are only found in sedimentary rocks, some of which are, indeed, made up of nothing else Mineralogical Basis for Sedimentary Rock Classification In the earliest classifications of rock, such as that proposed by Charles Lyell (see Famous Geologists: Lyell), four classes were recognized: volcanic, plutonic (these two are now grouped as igneous), metamorphic, and aqueous The aqueous rocks were subdivided into three groups: arenaceous, argillaceous, and calcareous The term ‘aqueous’ has long