ABSTRACT
Sedimentary rocks are composed of two major groups: Terrigenous clastic rocks and Rocks formed by precipitation from solution. Sedimentary petrography usually refers to the study of sedimentary rocks under the microscope. The primary division of terrigenous clastic rocks is according to average grain size. The most commonly encountered mineral grains are quartz and feldspar. Cement is the term used to denote the crystalline material precipitated in spaces between the grains. Most primary porosity in sedimentary rocks is intergranular where it is between the grains or intragranular if it lies within a grain such as a fossil fragment. Textural features of sediments such as grain shape and roundness can also be visually estimated from thin sections. The principal constituents of limestones are the organized grains made up of calcium carbonate known as allochemical components, micrite and sparite. Glauconite is a potassium iron alumino-silicate which forms in shallow marine environments and is widespread in sandstones and limestones.
