Types of Emeralds

Color is a critical factor in emeralds and constitutes about half of the emerald's value (clarity 30% and cut 20%).

• Hue describes the primary color and any other colors in the stone. Most emeralds are green hued with a bluish hue also visible, especially the better Colombian-type emeralds.
• Tone is the depth or darkness of the color as perceived by the eye.
• Saturation is the amount of hue present in any given color.

Depending upon where the emeralds come from, they can exhibit a wide range of color; i.e., Brazilian emeralds are usually lighter toned and less saturated than their Colombian cousins.

The green in the emerald is caused by the trace element of chromium. If the color is very light green, the stone is more correctly referred to as green beryl, not emerald.

Emeralds are often oiled to help their appearance. Normally an uncolored oil such as Merck cedar wood oil is used. The stone may soak in the oil for several days and will actually take the oil in somewhat, helping bring out the color and "wedding" on some of the dry inclusions, making the stone look better.

If one finds an emerald that is mild in color or has a grayish hue, it is a good bet to soak it in oil a couple days and it may regain its green color, not to mention its value.

A more unscrupulous improvement is to use dye or oil with color in it. It is possible to influence the color of a stone by having it soak up colored oil.

Other problems with buying emeralds are the fact that there are a  number of stones that look like emeralds and overlap colors. Tsavorite, a garnet found in Kenya and Tanzania, looks quite a bit like emerald and has a pure green hue, although it tends to be a little bit more yellowish and never has the blue hue of emerald.

Chrome tourmaline is another stone that looks much like an emerald with a moderately strong green color. Another emerald look-alike comes from Africa and is called chrome diopside. All these stones can, and are, sold as emeralds to the unwary.

Different emeralds from different areas tend to have individually shaped inclusions; i.e., slight pyrite inclusions are typical of emeralds from Colombia although they can be seen in stones from other sources.

A three phase inclusion that shows up under a 10x or stronger microscope, which has a distinctly liquid area, a gas bubble in a solid square rock crystal, salt lying superimposed on each other inside a jagged edged cavity, is typical of emeralds from Colombia and proves their natural origin.

Tropic emeralds from Colombia sometime exhibit six fine radiating arms of black carbon inclusions, spoke-like in appearance.  Another type of this stone has six arms of emeralds extending from the center of the crystal with a white shaped wedge area in between. When these stones are cut and mounted, they are valuable because of their inclusions.