Amethyst Galleries
Amethyst Galleries: Mineral Gallery: The Mineral Hornblende
Beginning with a list of physical characteristics, this resource explains hornblende is actually a series of minerals such as Magnesio-hornblende, Ferrohornblende, and Alumino-ferro-hornblende.
Wikimedia
Wikipedia: Hornblende
Wikipedia offers a description of the mineral Hornblende including specific gravity, hardness, and image.