For more info, the nice people at Rings and Things have just added a
gemstone information database:

http://rings-things.com/gemstone/index.html

That's an addition to the Links List right there; thank you. Also on the List:

Amethyst Galleries' Mineral Gallery
http://www.galleries.com/default.htm
"The Mineral Gallery is a constantly growing collection of mineral
descriptions, images, and specimens.......together with several ways of
accessing these descriptions."
~~
Sooz