Other
The image.com: Minerals
This is a very large list of minerals complete with image and physical descriptions, chemical descriptions, and classification.
Wikimedia
Wikipedia: Topaz
This encyclopedia article from Wikipedia provides a general overview of the gemstone topaz. Liinks are provided for additional information on related subjects.
Curated OER
The image.com: Minerals
This is a very large list of minerals complete with image and physical descriptions, chemical descriptions, and classification.