Gemstones

Birthstones

 

Garnets
Garnet January
Amethyst
Amethyst February
aquamarine
Aquamarine March
Diamonds-April
Diamond April
Emeralds-May
Emerald May
Pearls-June
Opal June
Ruby-July
Ruby July
Peridot
Peridot August
Sapphire-Sept
Sapphire September
Opal-October
Opal or Tourmaline October
Citrine-Nov
Citrine November
Topaz-December
Tourquise or Topaz December

 

Sapphires

Sapphire-Monica

Sapphires belong to the Corundum family. They are best known as blue, however in fact occur in just about every colour possible, including a deep pink. Its chemical composition is aluminium oxide, and crystal structure: trigonal, forming bi-pyramids. Hardness: 9 (so it is quite hard). Refraction I.: 1.762-1.770.

Blue sapphires are found in different parts of the world and vary enormously in quality and colour. The finest ones are considered to come from Myanmar (Mogok mines) and India (Kashmir). The Burma blue sapphires are a deep blue without any hint of mauve and have a great deal of life and brilliance. Kashmir stones are particularly fine and have their own colour range which is a bit difficult to describe: blue with a very slight milky appearance due to tiny inclusion of rutile needles what is called “silk”. The mines in Kashmir are at over 14,000 feet above sea level, and for much of the year are inaccessible due to the extremes of climate. Thailand is a major source of sapphires but they tend to be dark and duller blue, therefore they are not nearly as costly. Sri Lanka, produces probably the greatest amount of gem quality sapphires in the world, from the Ratnapura area. The characteristic colour is well known as “cornflower” blue, and they can be beautiful blue stones of great brilliance and size. Sri Lanka is also the main producer of fancy coloured sapphires: yellow, purple, green, pink and rare orange-peachy known as “padparascha”.

It is not usual to find a sapphire with the asterism effect. Star sapphires are translucent and have a base colour of greyish blue.

Australia is a producer of a large quantity of blue sapphires but they tend to be inky, over dark and usually have a greenish tinge. Other major producer is Montana in USA. These sapphires are easily recognisable for their intense steely blue. They rarely occur in large size but were used in art noveau period and 20th century jewellery.

The usual cuts for sapphires are: the step cut, brilliant cut, mixed cut and cabochon (for star sapphires).

First synthetic sapphires were made in laboratories by Verneuil process as are star sapphires. When viewed through a loupe or microscope, they normally show curved colour bands as opposed to straight bands in natural stones. Besides tiny gas bubbles may also be visible. Synthetic white sapphires are used sometimes to imitate diamonds.

Sapphires may be heated to intensify, lighten or darken their hues, to create or remove asterism or to chain their colour. This treatment is a very usual practice and universally accepted. Heat treatment, is widely regarded as the continuation of a natural process, since it only involves the application of energy and the resulting colours are usually stable.

Kindly supplied by   Monica G Saez   “Gemstone consultant and Jewellery valuer”

Ruby

Ruby1

Rubies belong to the gem species called Corundum. They occur in mines and alluvial deposits in conjunction with various precious stones. Chemical composition: aluminium oxide. Its crystal structure is trigonal, forming hexagonal crystals. Hardness: 9. Refraction index: 1.762- 1.770.

Ruby is coloured by chromium and its darker colour and brownish tint, in Siam is due to traces of iron. The finest stones come from the mines in the Mogok area, Myanmar. These stones are of a beautiful bright red, often referred to as “pigeon blood” red. Rubies from neighbouring Thailand, are not of the same colour and quality, tending to be darker, often with a brownish tinge, however the modern heat treatment effectively eliminates these hues, and commonly referred to as Siam rubies. Sri Lanka and India also produce rubies. Ceylon in particular produces a large quantity from the Ratnapura region, they tend to be pale and pinkish.

Ruby-Star

Opaque rubies with a weak star-effect are mined in Mysore, India.

The most usual cut is a combination of brilliant-cut crown and a step-cut pavilion and most stones are “native-cut”, faceted and polished by the miners at source. Facets are not uniform and the shapes of the cut stones are not symmetrical so these stones are easily discernible.

Unlike most gemstones, rubies do not occur in large sizes and stones of the finest colour and clarity seldom weigh more than a few carats. A 5 ct. stone of top quality is considered of importance and over 10 ct. is really a rarity

Synthetic rubies are made in laboratories, usually by the Verneuil process. They are distinguishable to an expert since they are too perfect, colour too good and they will show inclusions of tiny gas bubbles and none of the inclusions normally found in natural stones.

A particular inclusion in natural rubies is known as “silk”, under a jeweller´s loupe it looks like a very fine layer of white silk strands.

In medieval times when gemologically stones were not always distinguishable one from another red spinels were called “Balas ruby”. Red spinels are often doubled with glass or crystal in order to pass them off as rubies.

Rubies have always had superstition attached to them because they are the colour of the blood and the Far East where they are usually found they are considered to enhance the wearer´s divinity and protect him against illness.

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Most of the rubies found on the market these days have had some form of treatment applied to them. It´s extremely important that the rubies have their treatments correctly identified and listed as it can have a drastic effect on the price of the gem.

Some of the most common treatments are:

Glass filled: Low grade ruby is used that is full of cracks and fissures. Ruby is bleached, and then is heat treated with the addition of a liquid glass. This liquid penetrates the ruby and improves the clarity of the stone by reducing the amount of visible cracks on the surface. This treatment is not very stable as the temperature changes or ultrasonic cleaners can cause the lead glass to fall out of the stone. It´s important to take into consideration that a ruby treated with glass will be heavier than a ruby with no treatment.

Heat treatment: this technique has been used for centuries to treat rubies, to improve their clarity and colour. The heat will dissolve any rutile inclusions inside the stone which can enhance the red colour and improve the clarity of the stone.

Beryllium treatment: this treatment is more often used on Sapphires. The rubies are heated while beryllium is added to the crucible. It´s used to create a more intense red colour.

Kindly supplied by   Monica G Saez   “Gemstone consultant and Jewellery valuer”

Emeralds

EMERALD

EmeraldM1They belong to a gem species called Beryl, which also includes aquamarine (bluish-green), golden beryl (yellowish) and morganite (pink).  Chemical composition is beryllium aluminium silicate. The crystal structure is hexagonal, forming hexagonal prisms, Refraction I.: 1.56-1.60. Emeralds are green colour and usually found on their own, however the other three are often mined together. Although they are hard stones, almost 8 from the mohs hardness scale, they have a fracture property so that we could say they are some delicate. Emeralds always show inclusions and marks to the naked eye. An emerald with no inclusions, clean, should be treated with suspicion as it might be a synthetic. Emerald inclusions are often described as looking mossy or garden-like. They’re sometimes called “jardín,” which is Spanish for garden.

The most desirable emerald colours are bluish green to pure green, with vivid colour saturation and tone that’s not too dark. The most-prized emeralds are highly transparent. Their colour is evenly distributed, with no eye-visible colour zoning. If the hue is too yellowish or too bluish, the stone is not emerald, but a different variety of beryl, and its value drops accordingly. The intensity of the green in the finest emeralds might not be equalled by anything else in nature.
Chromium, vanadium, and iron are the trace elements that cause emerald’s colour. The presence or absence of each and their relative amounts determine the exact colour of an emerald crystal.

First emeralds found and mined originally in Egypt, although poor quality. The most famous and lasting source is in South America. The best quality emeralds in the world are coming from Colombia and were introduced in Europe for the first time after the Spanish Conquest. The main Colombian mines are called Muzo, Chivor, Peñas Blancas and Cosquez which supply top quality stones.

These mines are located in the state of Boyacá, and access is difficult.
Colombian emeralds formed through a hydrothermal-sedimentary process. The emeralds occur in organic rich shales and limestones.
Peñas Blancas emeralds are slightly bluish green, with little color zoning and a velvety appearance. One unique characteristic of the rough material is called “cascocho,” which refers to the crystals’ tendency to have pits and cavities due to secondary chemical etching. The abundance of quartz as a vein mineral differentiates Peñas Blancas from other emerald mines in the area.

Trapiche emeralds are perhaps the rarest and most mEmeraldM2emorable of “pattern” gems. Trapiche is the Spanish word for a spoked wheel used to grind sugar cane, which bears a striking resemblance to the pattern in these emeralds. Two distinct growth regimes are responsible for the formation. First, the central tapered core grows under hydrothermal conditions. Then, growth conditions change and both emerald and albite are formed. The hexagonal prism faces of the core maintain their uniform growth, producing pure emerald, while areas growing from the edges between prism faces do not and are filled with albite. This results in six sectors of clear emerald, and six of predominantly albite and minor emerald. Trapiche emeralds are cut into cabochons to display the beautiful spoke-like star.

Also, emeralds are mined in Brazil, (yellowish-green stones) but with a lower quality. Other sources are, Russia, Australia and Africa, Zimbabwe (excellent quality), Zambia (cooler, more bluish green colour) and Zaire. Other minor sources are Norway and USA.

Emerald gemstones are normally step-cut, well known as emerald-cut as this shows their natural colour to best advantage. Lesser quality stones may be cut as called “cabochon” or as beads.

Synthetic emeralds are laboratory made in the USA (some marked as Chatham emeralds). These emeralds have characteristic inclusions that are easily recognizable by an expert eye. Clear beryl and quartz doublets with a green coloured glue in the girdle area or with a green gelatine best known as “sandwich”, are also used as emerald imitation but easily discernible with a jeweller´s glass. Emeralds in general, show red through the Chelsea colour filter. The more presence of chromium, the redder the emerald will show through. This filter may be used as a rough guide to help identification.

EMERALD TREATMENTS. Most emeralds have not only numerous internal inclusions and fractures, but also tiny surface breaking fissures or cracks. For this reason, the vast majority of emeralds are treated to improve their clarity. This practice is widely accepted in the trade. The traditional treatment for emerald is oiling with cedar oil. Cedar oil is a natural product from cedar trees and is colourless and viscous. Cedar oil has been used for fracture-filling emerald because it has a refractive index that is similar to emerald.

Since cedar oil is so sticky, it is not easy for it to penetrate the microscopic cracks in emeralds so it requires some heat and pressure to do the job. Traditional oiling is stable but not permanent. Eventually an oiled emerald will require re-oiling to keep it looking at its best. Therefore, a number of attempts have been made to introduce more permanent fillers. These include natural and artificial resins (such as opticon), polymers and prepolymers. The use of these new fillers has created some controversy, particularly in cases when the exact filler has not been disclosed. One important thing that consumers want to know is the degree to which an emerald has been enhanced.

 

GOTA DE ACEITE (Spanish for Drop of Oil)

The finest and rarest emeralds are sometimes said to have an optical effect called “gota de aceite”. EmeraldM3This term describes an aspect of emerald clarity that is associated with Colombian emeralds. Gota de aceite describes a remarkable phenomenon that occurs very rarely and typically only in the finest emeralds Emeralds with this effect display a roiled appearance that is reminiscent of honey or oil—hence the name. The phenomenon has also been called the “butterfly wing effect”. The contribution of gota de aceite to the desirability of such stones is similar to that of the velvety effect in Kashmir sapphires. In both cases, the diffusion of light spreads the area of color, thus reducing extinction. It should also be noted that the gota de aceite effect in fine Colombian emeralds may appear somewhat similar to the roiled growth zoning observed in many hydrothermally grown synthetic emeralds, particularly those from Russia. Therefore, careful examination is important to avoid a potential misidentification.

Kindly supplied by   Monica G Saez   “Gemstone consultant and Jewellery valuer”