The International Gem Society: at http://www.gemsociety.org gives free, basic instruction in gemology, lapidary and jewelry making as well as providing a price comparison survey, a general reference section and a unique, "Gemology for Kids" section. For a small subscription fee, members receive a quarterly journal, "Color and Light" and have access to additional services such as a certification program.
Ganoksin Online: http://www.ganoksin.com - The gem and jewelry world's foremost information resource on the Internet. Open to the public, free of charge - a substantial library of articles, publications, reports, and technical data on gem and jewelry related topics; as well as a sizable collection of art and jewelry galleries, for both the casual visitor and the professional. The organization sponsors, for jewelers, lapidaries, dealers and other interested parties, one of the most widely read free newsletters/digests on the internet.
Gemological Institute of America (GIA): http://www.gia.edu - In addition to information about fees, format and content of it's world famous courses and programs, there is free information on diamond and gemstone news and research. There's also basic information on the 4 C's method diamond grading/evaluation in the on-line tutorial entitled "How to Buy a Diamond". There are links to GIA stores where a huge variety of books, videos and instruments can be purchased.
The American Museum of Natural History: has an information and photo packed website supporting its public exhibition on diamonds: http://www.amnh.org/exhibitions/diamonds/composition.html
The Mineral Galleries: a huge list of minerals by name, each of which links to a page with photos and detailed geologic and gemologic information: http://mineral.galleries.com/minerals/byname.htm
Gemology on Line, a wonderful reference for all aspects of gemology, gem collecting and jewelry has a well done glossary of jewelry terms at this link: http://www.gemologyonline.com/jewelry_dictionary.html
Gemology Tools: Gemology Tools is Windows software that contains the most complete gemology reference aids available. This program is intended for the gemologist, gemology student or anyone who loves gemstones. Included are such gemology aids as the Gemstone Database which gives you access to over 1,500 gemstone species, varieties, trade names and misnomers, diamond weight estimators, colored stone weight estimators, a pearl grader (based on the system developed by the Guide), a diamond cut grading system (devised by NAJA), a round diamond recutting analyzer and much more. The Gemstone Database provides over 35 facts, properties and characteristics for most gemstones. Over 750 gemstone photographs are included. The Gemstone Database also features the new Gemstone Separator, the easiest way to make a gem identification and the new Inclusion Gallery which provides you with numerous visual examples of gemstone and diamond inclusions and surface features. Cost is $29.95 to $69.95 depending on whether you order the Student or Professional Version, and and on whether you select the download or CD option: http://www.gemologytools.com