Emerald Gemstones
The Green colour of emerald is caused by traces of chromium (Cr), although vanadium (V) may also be present in some stones. Trapiche emerald – trapiche emerald crystals from colombia are of several types and usually display a six-rayed radial structure. Commonly, they consist of a central hexagonal green crystal from which six segments of similar colours have grown outwards. A fine-grained mixture of colourless beryl and feldspar fills the radial spaces.
Emerald is the birhtstone for may.
In the 1914 book The Book of Talismans the author writes of emerald: “If worn in a ring, emerald strengthens the memory and protects from giddiness.” It was also said to guard sailors and fisherman from perils and mishaps at sea if suspended “round the neck so as to lie upon the chest”.
Durability and fashioning
Emerald is a very brittle stone usually containing fissures and is easily chipped. It shoud never be put in an ultrasonic clearner, but washed in mild soapy water. It should not be left to soak in detergents of solvents. Although cut in various styles, a common cut for emerald is a rectangular step cut, with the corners truncated to give an eight-sided (octagonal) outline.
This has been used so extensively for emerald that it is often called the emerald cut. This brittleness can also influence the design and setting of emerald set jewellery.
General Care
Emerald, can fracture easily. Avoid wearing whilst doing anything that could cause the stone to be knocked. Do not allow emeralds to come into contact with solvents as these can affect any fillers that may have been in the stone.
Workshop Care
- Avoid:
- Heat which can cause fracturing in included stones and the evaporation of any fillers
- Detergents
- Ultrasonic and steam cleaners.
Localities and inclusions
Emeralds are found in colombia, Brazil, India, Pakistan, Siberia, South Africa, Zambia and Zimbabwe. Almost all natural emeralds contain inclusions, and these are very important in distinguishing natural from synthetic emeralds and other green stones. However, some growth features such as straight colour zoning are seen in both natural and synthetic emeralds.
Some inclusions are common for particular localities.This, when combined with an assessment of RI and SG, may provide an indication of the country of origin (to be covered in more detail in the IDT Graduate Gemologist Diploma Course)
| Locality | Comments and inclusions |
|---|---|
| Colombia | Three-phase inclusions (liquid-filled cavity containing a crystal and a gas bubble). |
| India | Two-phase inclusions (liquid-filled cavity containing a gas bubble). |
| Zimbabwe | Tremolite (usually fibrous or needle- like a crystals). |
| Siberia | Needle-like crystals of actinolite. |
| Many Localities | Mica flakes, pyrite and calcite, and also colour zoning. |
Common treatements
Many commercial emeralds are treated with oil or polymer resin, which fills those fractures (cracks and fissures) which reach the surface. This hides the fractures and temporarily enhances the appearance by improving clarity and colour. Ultrasonic cleaning will usually remove oil, replacing it with dirty cleaning fluid which dries in place and spoils the stone.
The detection of oil is not easy. Microscopic examination may reveal interference colours in the fractures. Also fractures may not be completely filled by the oil, and gaps may be visible. Before cleaning a stone, look for traces of oil on the surface and for oil marks within the stone packet. Some oiled stones may have been treated with substances that fluoresce in UV light.
The detection of polymers is difficult because the RI of the polymer is very close to that of the emerald. Very careful examination of the surface under magnification may reveal the fracture. By rotating the stone a coloured flash of light may be seen reflected from the filled fracture. This can be orange, blue or another colour, depending on the filling.
Dyeing
Emerald is sometimes dyed to improve the colour. The treatment may be identified by the concentrations of dye in cracks in the material.
Materials with a similar appearance
Similar looking material include green tourmaline, YAG, glass, aventurine quartz, dyed green quartz, GTD’s and soude stones. In facts almost any green material of similar colour has been used to imitate emerald either in its rough or cut form at some time. A common rough simulant is a composite green glass and blackish matrix material, however composites have also been made up using low-grade emeralds.
Tests
Dichroscope- Weak to strong—blue –green and yellow-green; dichroic.
UV and filters— some emeralds fluoresce pink or red under UV and appear pink or red through the CCF. This is not diagnostic as some emeralds, mainly from India and Africa, remain green due to traces of iron which quench the fluorescence.
Note: Although the CCF was first created to help identify emeralds, today it can be used as an indicator test only and further testing would be required.
Spectrum— A typical emerald spectrum has fine lines in the red, a weak general absorption in the yellow-green and a weak line in the blue.
Quality Factors
The depth and tone of colour of emerald are very important with a rich soft green being most highly regarded. Most emeralds do have inclusions, many being heavily included. The better the clarity, the higher the value, but the clarity of emerald should not be compared to that of stones such as aquamarine. Locality is still a major price factor with most emeralds. The stones below are in order of value per carat, with the highest value on the left.