Nothing is as important in the natural world as our own earth and the rocks beneath our feet. So it was inevitable that the Golden Nature Guides include an introduction to rocks and minerals. The task of selecting, describing, and illustrating minerals,  rocks,  and  geologic  structures  has many  inherent  difficulties.  We are grateful  to  our  colleagues and to other experts who have helped. May we particularly thank members of the Geology Department of the University of Illinois: Drs. Chapman, Droste, Grim, Hagner,  Henderson,  Merrill,  Wanless,  and  White,  and Drs. Collinson, Swann, and Willman of the Illinois State Geological Survey for specimens and slides, and for information  and   encouragement.   Some  specimens  came from University of  Illinois Natural  History Museum  and departmental collections; some from Ward's Natural Science Establishment. The gem collections at the Chicago Museum of Natural History were invaluable. Fine Koda-chromes were provided by Scott Lewis. Maps came largely from information in the Minerals Yearbook of the Bureau of Mines, and from other maps and publications of the United States Geological Survey.

The term geology is a combination of two Greek expressions: “Geo” refers to the earth, and “logos” refers to the logic and language used to explain your observations. So think of geology as a way to organize and explain the earth processes that we see all around us. For some of the strange shapes we see, an educated explanation would be great. Most of what we know is good guesswork, based on lab experiments and inferences that take many detailed drawings to explain and a lifetime to understand. Fortunately, the more you see, the better things fall into place. <...>

Our understanding of the mechanisms by which organisms fonn minerals has progressed in the past two decades but is still at a rudimentary stage. Any general theory of biomineralization must explain the formation of solid phases from biological fluids in tenns of physical parameters such as supersaturation, ionic strength, pH, surface energies and the character and quantity of active sites. Knowledge of the functions of the organic matrix' in mediating mineral deposition is of basic importance to any understanding of biomineralization..