Other
The image.com: Minerals
This is a very large list of minerals complete with image and physical descriptions, chemical descriptions, and classification.
Jewelry Central
Jewelry Central: Gemstones
This commercial site contains general information on various synthetic and natural gemstones and provides links to specific gems.
Curated OER
The image.com: Minerals
This is a very large list of minerals complete with image and physical descriptions, chemical descriptions, and classification.