Cat's eye

A cat's eye like effect, known as 'chatoyancy', appears to move on this stone's surface. Cat's eye is a gem variety of chrysoberyl. 

Hardness: 8.5 on the Mohs' scale.

There are generally two varieties of cat?s eye ? the alexandrite cat?s-eye and the chrysoberyl cat?s-eye, which is very popular in the Far East, particularly in Japan. The ideal colours of the chrysoberyl cat?s-eye are yellowish-brown, which is called the honey colour, and the yellow-green, which is called the apple green colour. A very good cat?s eye, apart from being of ideal colour, should have a high degree of transparency and a well-defined unbroken ray. It should be free from any distracting inclusions visible to the unaided eye. The chrysoberyl cat?s-eye is one of the most beautiful gemstones because of the ?chatoyancy? or the eye effect. 

Description 
A translucent variety of chrysoberyl (beryllium aluminum oxide) which exhibits a silvery white line across the stone. This moves as the stone, the light source or the observer moves and may appear to open and close like an eye. The finest quality has a sharp eye that appears to open and close as the stone is rotated, and exhibits a strong "milk and honey" effect (stone on one side of the eye appears lighter than the other). These colours switch as the stone or light source is moved. The most highly prized body colours are greenish-yellow and brownish-yellow (honey colour). 

Varieties 
Rare specimens also exhibit change of colour. 

Sources Sri Lanka, Brazil. 

Phenomena 
Chatoyancy caused by the reflection of light off minute, parallel, needle-like rutile crystals or hollow tubes. 

Toughness 
Excellent 

Miscellaneous 
When a gem specimen exhibits both chatoyancy and change of colour, one or both phenomena will suffer. It is more common to find a good eye with poor change of colour. The conditions necessary for one phenomenon conflict with those needed for the other. The term cat's eye when used alone refers to chrysoberyl. Other minerals exhibiting chatoyancy must be qualified, e.g. tourmaline cat's eye. 

History 
Cat's eye has been regarded as a preserver of good fortune. The natives of Sri Lanka still consider it a charm against evil spirits. British royalty often use it as an engagement stone. 

Cuts & Uses 
Must be cut in a cabochon to produce cat's eye effect. This should be cut so that the long portion of the cabochon is 90 degrees to the direction of the needles.

 

Chrysoberyl

The species name chrysoberyl is given to a transparent, faceted gemstone that does not show a color change between daylight and artificial light (the chrysoberyl which shows a color change is called alexandrite). The ideal colors of chrysoberyl are green and yellowish-green. In addition, due to strong dichroism, one may see an 
attractive bi-coloured chrysoberyl occasionally. Hardness is 8.5 on the Moh's scale. The high refractive index of the stone makes it very lively when properly cut and polished

Star Stones

Star stones of the corundum family are either star sapphires or rubies. When light falls on these stones, a star effect is visible (known as asterisk). 

Sri Lanka is the best known source for star sapphires and star rubies. Star sapphires range in color from grey to bluish-Grey and from medium blue to medium dark blue. The very slightly purplish medium dark blue is the best color grade for star sapphires. Star rubies range from light pink-red to purple-red through deep purple-red. The intense red star rubies are extremely rare. A good quality star stone should have a high degree of transparency and a well defined star with no weak or missing rays. It should be reasonably clean and in the face-up position, no distracting inclusions or cracks should be seen. There should be no excess weight at the bottom of the stone. 

Star sapphires and rubies are hard stones (9 on the Moh?s scale), which can take a high degree of polish and retain the shinefor a long time. The special optical phenomenon of a well-defined six-ray star is a fascinating sight. The wearable qualities of the star stones make them suitable for men's rings.

Alexandrite

History 
Alexandrite received its name because it was discovered on the birthday of 
Czar Alexander II of Russia in 1830. Red and green are also the colors of the Russian Imperial Guard. 

Cuts & Uses 
Alexandrite is usually faceted. Chrysoberyl cat's eyes must be cut en cabochon to display a chatoyant effect.

Ruby

Ruby is an aluminum oxide, a variety of corundum; it occurs in medium to dark tones of red and violetish-red to brownish-red

Varieties 
Star ruby 

Sources 
Sri Lanka, Burma, Thailand, Africa (Kenya, Madagascar, Tanzania), India. 

Toughness 
Excellent, except in laminated or fractured stones. 

Treatments 
The Burmese believed that "blazing red" stones could be found in a "bottomless" valley. Natives threw pieces of meat into the valley, hoping that some stones could then be recovered by killing the vultures. In the Royal Collection of England, you can view a gold ring set with a pale but nearly flawless ruby into which a portrait of Louis XII of France is carved. 

Cuts & Uses 
Faceted or en cabochon, usually mixed cut (brilliant crown, step-cut pavilion), beads, carved (poor quality). 

Choosing a Ruby

The most important factor in the value of a ruby is color. The top qualities are as red as you can imagine: a saturated pure spectral hue without any overtones of brown or blue. The word red is derived from the Latin word for ruby, ruber, which is derived from similar words in Persian, Hebrew, and Sanskrit. The intensity of color of a fine ruby is like a glowing coal, probably the most intensely colored substance our ancestors ever saw. It is no wonder they ascribed magical powers to these fires that burned perpetually and never extinguished themselves.

Besides color, other factors that influence the value of a ruby are clarity, cut, and size. Rubies that are perfectly transparent, with no tiny flaws, are more valuable than those with inclusions, which are visible to the eye. Cut can make a big difference in how attractive and lively a ruby appears to the eye. A well-cut stone should reflect back light evenly across the surface without a dark or washed-out area in the center that can result from a stone that is too deep or shallow. The shape should also be symmetrical and there should not be any nicks or scratches in the polish. Rubies and other gemstones are sold per carat, a unit of weight equal to one-fifth of a gram. Larger rubies, because they are more rare, will cost more per carat than smaller stones of the same quality. 

The Ruby sometimes displays a three-ray, six-point star. These star rubies are cut in a smooth domed cabochon cut to display the effect. The star is most visible when illuminated with a single light source: it moves across the stone as the light moves. This effect, called asterism, is caused by light reflecting off tiny rutile needles, called "silk," which are oriented along the crystal faces. 

The value of star rubies and sapphires are influenced by two factors: the intensity and attractiveness of the body colour and the strength and sharpness of the star. All six legs should be straight and equally prominent. Star rubies rarely have the combination of a fine translucent or transparent color and a sharp prominent star. These gems are valuable and expensive.

The most famous source of fine rubies is Burma, which is now called Myanmar. The ruby mines of Myanmar date back to centuries ago: stone age and bronze age mining tools have been found in the mining area of Moog. Rubies from the legendary mines in Mogok often have a pure red color, sometimes described as "pigeon's-blood", although that term is more fanciful than an actual practical standard in the trade today. Myanmar also produces intense pinkish red rubies, which are vivid and extremely beautiful. Many of the rubies from Burma have a strong fluorescence when exposed to ultraviolet rays like those in sunlight, which layers on extra color. Burma rubies have a reputation of holding their vivid color under all lighting conditions. 

Sri Lankan stones are often pinkish in hue and many are pastel in tone. Some, however, resemble the vivid pinkish red hues from Burma. Rubies from Kenya and Tanzania surprised the world when they were discovered in the sixties because their color rivals the world's best. Unfortunately, most of the ruby production from these countries has many inclusions, tiny flaws that diminish transparency. Rubies from the African mines are rarely transparent enough to facet. However, their fantastic color is displayed to full advantage when cut in the cabochon style. A few rare clean stones of top quality have been seen. 

Occasionally a few fine, top-quality rubies appear on the market from Afghanistan, Pakistan or the Pamir Mountains of the Commonwealth of Independent States. The terrain in these areas has made exploration for gemstones very difficult but someday they may produce significant quantities for the world market.

Sapphire

Sapphire is an aluminum oxide. Its color varies from very light to dark blue to Violette-blue, bluish-green, yellow, slightly reddish-orange, brown, nearly opaque black, colorless, pink, violet and the pinkish-orange padparadscha (lotus flower).

Varieties 
Coloured varieties, star sapphire, alexandrite-like sapphire. 

Sources 
Sri Lanka, Kashmir (India), Burma, Thailand, Australia, Tanzania, Kenya, Montana, Madagascar 

Toughness 
Excellent, except in laminated or fractured stones. 

Precautions 
Sapphires may fade if heated 

Treatments 
Sapphires can be x-rayed to intensify their color. Natural sapphires undergo heat and diffusion treatments in Thailand. With the first method, sapphires with latent chemical components for good color are "ripened" to a desirable color through heating. In diffusion treatment, sapphires that lack the components for good color are placed in a bath of coloring oxides that penetrate the outer layers of the stone. Treatment of blue stones is permanent. 

History 
According to an ancient Persian legend, the earth rested on a great sapphire whose reflection was seen in the sky. The stone also appears in the Promethean legend. Prometheus was chained to a rock by Zeus for having stolen fire from the gods. After being rescued by Hercules, a link of the chain remained on his finger, and attached to it was a piece of rock. Zeus agreed to grant Prometheus his freedom if he wore the link as a reminder of his sin. Later a ring set with a sapphire replaced the link and stone. Sapphire symbolizes truth, sincerity and constancy. It was believed to protect the wearer against capture by an enemy, and to win the favor of princesses. It also protected against poison. It was said that if a poisonous snake were put in a vessel with a sapphire, the rays from the gem would kill it. The name sapphire originally comes from Sanskrit. It became sapphires in Greek, meaning blue. Before the value of sapphire was known to them, villages in the Zanzibar mountains of Kashmir (India) used the gem as a flint to start fires. 

Cuts & Uses 
Faceted and en cabochon, usually mixed cut, beads, carved (poor quality). Synthetic sapphire is used in watches, precision instruments and electronic equipment.

Pink Sapphires

SAPPHIRES ARE NOT JUST BLUE

In recent years, due to the popularity of pink diamonds that are one of the most rare & expensive of all gemstones, the Pink Sapphire has grown in popularity.

Blue has been the most ‘classic’ color for sapphires, Pink Sapphires are far more rare & why the blue sapphire was so widely used. Demand for pale pink gemstones in jewelry has created a market for this stone, with the shade of pink varying from the palest of pinks to a deep fuchsia. Sapphires are available in yellow, violet, blue, green, colorless & of course blue.