The Emerald Story

How does a novice differentiate between the natural and synthetic emeralds?
1. Refractive index (R.I): The refractometer is an instrument which measures the R.I of a gemstone. The R.I of a natural emerald tend to lie between 1.570 – 1.590. However, the R.I of a flux-grown synthetic emerald tend to be slightly lower, 1.563-1.566. This might be the first indication as to the authenticity of the stone, however. Care should be taken as some rare natural emeralds may also have low R.I readings. Hydrothermally grown synthetics will have R.I’s in the same range as natural stones.

2. Specific gravity (S.G): Specific gravity can be estimated using indicator liquids, or precisely using the hydrostatic method. The S.G of natural emerald is usually in the area of 2.7 – 2.8. Flux grown synthetics generally have a low S.G in the area of 2.66. Hydrothermally grown synthetics will have S.G’s in the same range as natural stones.

3. Inclusions under magnification: The nature of certain inclusions can indicate to us that an emerald is real or synthetic.
Natural emerald: Two or three phase inclusions, mineral inclusions such as calcite, pyrite, and mica, etc.
Synthetic emerald: Wispy veils of flux feathers, arrow head zoning, fine ling structural zoning, etc.

4. Chelsea Filter: A simple hand-held instrument, designed originally differentiate between emeralds and other green simulants. When viewed through this filter, a natural emerald appears anywhere from green to light pink, to red, depending on the chromium content in the stone. The more the chromium present, the more red it appears under the filter. On the other hand, many synthetic emeralds appear a striking or (hot coal) red under filter. Today many synthetic emeralds have been deliberately produced with a lower chromium content so this test should be used only with caution.

5. Others: More sophisticated means of identification are available to the lab gemologist, such as infra-red spectroscopy, and energy dispersive x-ray fluorescence. Therefore, if doubt exists, the stone should be submitted to a reputable gem testing laboratory for examination.

Imitations of emerald (natural or man-made)
An imitation of a gemstone is a material (natural or otherwise) that has same general appearance as the gem it imitates, but does not have the same chemical and/or physical properties, i.e. an imitation stone only looks like the gemstone it imitates. Some of the materials that might be mistaken for emerald are the natural gems: green tourmaline and peridot, the altered gems: dyed agate, dyed green quartz, and green glass.

Identification: The properties of these imitations differ markedly from those of natural emerald, e.g. R.Is, S.G’s, and inclusions. It should therefore be relatively easy to differentiate between these and natural emeralds.

Examples of possible imitations of emeralds and their properties

Green tourmaline
R.I = 1.62-1.64
S.G = 3.05
Inclusions = Flat liquid-filled feathers, growth tubes, etc.

Peridot
R.I = 1.65 – 1.69
S.G = 3.34
Inclusions = Lily-pad-like inclusions, etc.

Jadeite (green)
R.I = 1.66
S.G = 3.33
Inclusions = Granular appearance, etc.

Dyed Green Quartz
R.I = 1.544 – 1.553
S.G = 2.65
Inclusions = Concentration of dye in cracks, etc.

Green Glass
R.I = 1.44 – 1.69
S.G = 2 – 4.2
Inclusions = Gas bubbles, swirl structures.

Composite stones
More common imitations of emerald are composite stones or as they are often referred to doublets/triplets. Doublets have the appearance of one whole stone but are an assembly of two pieces of stone using a colored adhesive. Generally, the junctions of the two pieces may be seen in the area of the girdle (however, with garnet-topped doublets this may not be the case). The most common emerald doublets are formed using two pieces of colorless beryl to form the top and bottom, and these are cemented together with a green colored layer in the area of the girdle.

Identification: Composite stones are easily detected upon immersion in a liquid. The green junction is easily visible dividing the top and bottom when the stone is viewed, with a lens or microscope, in profile.

The grading of emerald
As with any other gemstone, the four C’s determine the value of emerald. These are color, clarity, cut and carat weight.

Color: This is the most important determinant of value. An included stone with good color will fetch a higher price than a clean stone with a weak color. Deep, pure green is desirable. Any variation of the green shade can fetch a good price provided there is depth of color.

Clarity: Emeralds are characterized by the fact that they almost invariably contain inclusions. It is very hard to find a flawless emerald with the desired color. The location of the inclusion plays a vital role in the valuation. If a flaw is very prominent on the crown of the stone, it could bring down the price. But if the same flaw were present in a more subtle position, the ultimate value would not be affected.

Cut: The depth of color and apparent clarity of a gemstone is to a certain extent the function of its cut. A well cut stone could improve the depth of color and mask certain flaws, thereby upgrading the stone. The emerald cut is ideal for emeralds for a given quality. Depending upon the number of inclusions and color, other cuts are employed, e.g. cabochons, beads, rounds, hearts, fancy cuts, etc.

Carat weight: The value of a gemstone is calculated by multiplying price/carat into total carat weight. Hence, the more the weight, the higher the potential return. Size also affects the price per carat. This is because it is very rare these days to find a large-sized emerald of an acceptable quality. Given two stones of the same quality, the one significantly larger will fetch a higher market price per carat. If two stones are of the same size and quality and thus form a pair the price per carat of the pair jumps up.

How the market operates
There is no centrally operated and controlled market for emeralds, as one has for diamonds. The mining process is largely carried out by private companies in most countries, and a few mines are run by governments. The rough stones procured are cleaned and sorted into parcels by the mine owners. The main mines are in Colombia and Brazil. Buyers come from all over the world to bid for and buy these rough parcels. These are then taken to the cutting and wholesale centers in New York, India, Israel, Germany, Hong Kong among others. Wholesale and retail buyers from all over the world come to these centers to buy faceted emeralds. These are subsequently set in jewelry and sold to the ultimate consumers.