We get a variety of rocks, minerals, and crystals from traders at SMM's Collector's Corner. Sometimes we need reference books or use the internet to identify specimens. Webmineral.com has the most comprehensive mineral image library on the web. Their pictures of over 2,700 different species represents 60% of all known minerals. This mineral database contains 4,442 individual mineral species.
To differentiate minerals, several properties need to be identified.
The section on crystallography has a tool that allows you to see crystals from any angle by using the computer mouse. Another section gives chemical composition, or to see all minerals that contain a certain element. The search tool allows one to enter several properties with the most relevant finds placed first in the results.
The "Collectors Corner" of the Mineralogical Society of America features an excellent, on-line, mineral identification key by Alan Plante, Donald Peck, & David Von Bargen. Their identification key is also based on simple mineralogical tests such as luster, hardness, color and physical description for the most common minerals an individual is likely to encounter.