EARTH MATERIALS: This site is dedicated to the study, use, and forensic investigation of earth materials.
 
"Geologists are 'scientists' with an unnatural obsession with geology (rocks and alcohol). Often too intelligent to do monotonous sciences like biology, chemistry, or physics, geologists devote their time to mud-worrying, volcano poking, fault finding, bouldering, dust-collecting, and high-risk colouring." (Wikipedia)
 
Other Interesting non-professional Books: http://www.allbookstores.com/Nature/Rocks_and_Minerals.html)
Minerals of the World (2008; by Walter Schumann)
Gems & Minerals (2008; by Andreas Landmann)
Rocks and Minerals - Smithsonian Handbooks by Chris Pellant
The Book of Stones - Who They are and What They Teach by Simmons & Ahsian
Field Guide to Rocks and Minerals - National Audubon Society by Charles W. Chesterman
Rocks and Minerals - Eyewitness Explorers by Steve Parker  
Simon & Schuster's Guide to Rocks and Minerals by by Annibale Mottana, Rodolfo Crespi and Giuseppe Libori
 
 
BOOKS FOR STUDENTS:
Earth Materials: Minerals & Rocks (2001; by Gautam Sen; http://www.universityreaders.com
This is a textbook for undergraduate students. It was originally published by Prentice-Hall and copies can still be bought from the above link. A revised edition is expected to be published in 2009.
 
Earth Materials (1969; by W. G. Ernst) This book is out of print but can be bought from various sites including ebay. It is still a favorite for the old-timers.