The Mineralogy Database was last updated on 9/5/2012 and it contains 4,714 individual mineral species descriptions with links and a comprehensive image library. Visit the "What's New" section for details.
Each mineral has a page linked to tables devoted to crystallography, crystal structures, X-Ray powder diffraction, chemical composition, physical and optical properties, Dana's New classification, Strunz classification, mineral specimen images, and alphabetical listings of mineral species. There also are extensive links to other external sources of mineral data and information.
May I recommend the world-class book by Ron H. Vernon (2004): A practical guide to Rock Microstructure .-- Cambridge University Press.
ISBN 0 521 81443 X - ISBN 0 521 89133 7 (paperback).
The hundreds of microscopic images are explained in detail in both the captions and the text. The book also contains a huge list of references and a detailed index.