Introduction

Sandstones make up nearly one-quarter of the sedimentary rocks in the geologic record. They are common rocks in geologic systems of all ages, although their abundance and composition vary from system to system. They are distributed throughout the continents of Earth, and they form under a wide range of depositional conditions in a variety of depositional environments. Sandstones contain many kinds of sedimentary textures and structures that have potential environmental significance, as discussed in the preceding two chapters.

Particle composition is also an important aspect of these rocks; it is a fundamental physical property of sandstones and is the chief property used in their classification. Also, particle composition has significant value in interpreting the provenance history of siliciclastic deposits (Chapter 7). Particle composition may also influence the economic importance of sandstones as oil and gas reservoirs because particle composition has an important effect on the course of diagenesis in sandstones (Chapter 8) and thus on the ultimate porosity and permeability of these rocks.

Because of the relatively coarse grain size of sandstones, their particle composition can generally be determined with reasonable accuracy by using a standard petrographic microscope. Therefore, petrographic microscopy has remained for many years the primary tool for studying the composition of sandstones. Newer tools for studying particle composition are available also. X-ray diffraction techniques are used to determine the mineralogy of very fine-grained sediments.