Evaluating a Diamond: Color -
 Use this information to learn how diamond color is judged. Includes visuals to aid understanding. Also discusses factors that affect color perception.
http://www.diamondexpert.com/articles/color.html

Gem Gallery - The Image.com -
 Photos of gemstones, each accompanied by a description of the gem's properties and where it is commonly found. Includes instructions for close-up gem photography.
http://www.theimage.com/gemstone/gemstone.html

Gemological Institute of America (GIA) -
A nonprofit organization that offers gemstone identification and buying advice to consumers and training to those in the jewelry trade. The GIA provides lab services to the jewelry industry.
http://www.gia.edu

The Guide to Buying Fine Jewelry Online -
 Provides information on how to choose, buy and care for fine jewelry, from diamonds, pearls, precious gems, semiprecious gemstones, platinum, yellow and white gold to sterling silver.
http://www.anyamani.com

Guide2jewelry -
Buying tips and facts about diamonds, colored gemstones, pearls, and jewelry.
http://www.guide2jewelry.com/

The House of Tibara -
 Facts about opal include chemical make-up, buying advice, cutting and polishing basics, and opal care. Includes photos of different types of opals.
http://www.opal-tibara.com/

How Stuff Works: Moissanite Jewels -
 Five-part, illustrated guide that discusses the origin of natural Moissanite and explains how it is being created in the lab today.
http://www.howstuffworks.com/moissanite.htm

Idazzle.com -
 Provides basic information to help familiarize buyers with the qualities they should look for when searching for a diamond.
http://www.idazzle.com/