Province of British Columbia
B.c. Ministry of Energy and Mines: Common Rock Forming Minerals
There are six common minerals most often found in rocks. They are quartz, feldspar, olivine, mica, pyroxene, and amphibole. This website provides photos and information on each, and discusses their importance when identifying rocks.
University of Oregon
Ask Geo Man: Igneous Rock Forming Minerals
Ask GeoMan lists Olivine, Pyroxene, Amphibole, Feldspar, Mica and Quartz, as five common rock forming minerals. Characteristics of each are also given.
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.