When identifying a gemstone, a gemologist will want to hold it, feel it, and examine it from all angles. This is done to assess the appearance of the stone: the luster, the color, and any other features. A hand-held loupe may be used to search for scratches and flaws on the surface which may give an indication of hardness, while a scratch inside the stone may reveal characteristic inclusions. These features may be unique to one gem, but further tests may be necessary to identify synthetic or imitation stones. From this initial examination, however, the gemologist should know which tests to perform.
This key puts all gems into one of seven color categories, though color varieties within some species may appear is more than one. Each color category is divided into three sections: gems that are always that color, gems usually that color, and gems sometimes that color.
Many gems appear the same color, but can be distinguished when viewed with a spectroscopy. This reveals an absorption spectrum that is unique to each gemstone.