University of Kentucky
University of Kentucky: Kentucky Agate
Has information on agate which is Kentucky's official state rock. There are links to different close-up pictures of Kentucky agate.
Other
The image.com: Minerals
This is a very large list of minerals complete with image and physical descriptions, chemical descriptions, and classification.
Amethyst Galleries
Amethyst Galleries: The Mineral Quartz
This resource provides a description of the mineral quartz, including physical characteristics and color images.
Curated OER
The image.com: Minerals
This is a very large list of minerals complete with image and physical descriptions, chemical descriptions, and classification.