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Color
A stone should be examined in three directions: face up, face down and a profile view. You should examine a stone to see what color hue it is, which you can do with the aid of a color chart. You should also examine stones to determine the range of the tone level, which is from very light to very dark. Color identification, however, is not the best way to identify a stone because some stones, such as a sapphire, are found in different shades. Another example, the diamond, is the same color as a cubic zirconium and can only be differentiated when closely examined.
Transparency
The transparency of a stone--whether it is opaque (lapis lazuli), semitransparent (amber), transparent (diamond), semitranslucent (star garnet) or translucent (chalcedony)--is another way of identifying gems. An opaque stone isn't able to transmit light through it; a transparent stone can transmit light. Transparent stones allow gemologists to view objects through the stone to make a proper identification.
Cut
The terms used to describe the cut of a stone include faceted, cabochon, cameo, emerald, princess, bead, heart, round, brilliant, step, mixed and tumbled cuts. Certain stones are usually cut in a particular way, making it a good way to indicate the type of stone being examined. Rubies, for example, are often cut into cabochons, and princess cut is a popular shape for diamonds.
Phenomena
Being able to display phenomena is the term that is used to describe the ability to observe optical effects. Knowing what type of phenomena is occurring when examining a stone such as sheen, opalescence, asterism, change of color, play of color and iridescence can help in the stone's identification.
Luster
Luster is described by the quality and intensity of light reflected off a gem's surface. Levels of luster include adamantine (diamond), metallic (hematite), vitreous (topaz), greasy (garnets), resinous (amber), waxy (turquoise), dull (malachite), silky (tiger's eye) and pearly (pearl).
Dispersion
Dispersion is gem's ability to bend white light into a spectrum of colors, which, when visible, is referred to as fire or sparkle. Fire is categorized as being weak, moderate, strong or extreme. The amount of fire is examined by using a penlight or other source of concentrated light.
Heft
Heft refers to the weight of a stone compared to its size with each stone having a specific gravity indicated by a number. Heft is identified by holding the stone to determine whether it is light, medium or heavy in weight. Those who are experienced in identifying heft can easily distinguish, for example, aquamarine from blue topaz or a diamond from a synthetic cubic zirconium.