Introduction

Geochemists have used the term geochemical spheres to describe the various parts of the earth being studied. Various methods of geochemical prospecting using biosphere materials have been used. Groundwater geochemical research involving the lithosphere includes studies of concretions such as gypsum, barite, chert, and agate; red beds; opal and turquoise deposits; uranium deposits, particularly roll fronts; dolomitization; and caliche formation. The hydrosphere contains the drinking water of the world. The decay of soil organic matter provides the largest CO₂ input into the atmosphere. The decay of soil organic matter provides the largest CO₂ input into the atmosphere. Coal may be used directly as a fuel or indirectly as a nonfuel to produce a more convenient or more efficient fuel by carbonization, gasification, or hydrogenation. The chapter also presents an overview of the key concepts discussed in this book.