This book provides an introduction to the study of the solids that make up planet Earth. These materials consist of naturally occurring chemical compounds, known as minerals, and their aggregates, rocks. Only through the study of minerals and rocks can we learn about the history of the Earth, and this knowledge is also important because of the extensive use made of Earth materials in everyday life, such as the fabrication of tools; the manufacture of vehicles; and their use as construction materials, sources of energy, and soils for agriculture. This knowledge is clearly important in the search for mineral resources, but the general public needs to know the finite nature of many of our natural resources to make informed decisions.
Many different processes are involved in forming a rock from a group of minerals. These processes are normally divided into three general categories: ones involving molten material, which we call igneous; ones involving the weathering of rock and transport of sediment, which we call sedimentary; and those that modify rocks through changes in temperature, pressure, and fluids inside the Earth, which we call metamorphic . Throughout the book, we first introduce how to identify the minerals that are common in each of these main types of rock, and then we discuss the processes that lead to the formation of those rocks. These processes, many of which are intimately related to plate tectonics, have played important roles in the evolution of the planet.
In the following chapters, we deal with these main types of Earth materials, but in this first chapter we look at where the materials that constitute the Earth came from, and we then review the Earth’s major structural units. The wide compositional range of the many minerals and rocks found on Earth must in some way reflect the composition of the Earth as a whole. It is natural, then, to wonder where the chemical elements that constitute the Earth came from and what determined their abundances.