There are several key characteristics that define a high-quality emerald. Most important are color and clarity. The best emeralds are pure and a very bright green with no more than a slight hue of yellow or blue. Tone is judged by the depth of the color, ranging from colorless to black. Emerald tones are described as “light,” “medium light,” “medium,” “medium dark” and “dark.” An emerald’s clarity refers to the absence of inclusions. The rarest emeralds have no inclusions, although inclusions are acceptable and even expected by knowledgeable emerald buyers.
When buying an emerald, be sure to ask about the cut of the emerald and its size. Cut refers to the proportions that are used to produce brilliance in emeralds. The carat weight of emeralds, unlike diamonds, does not necessarily provide an accurate measure of the gemstones©ˆ size. Different gemstones have different densities (mass per unit volume), so two gems that appear to be the same size may actually have very different weights. For example, a ruby is denser than an emerald, so a 1-carat ruby will look smaller than a 1-carat emerald of the same shape.