Star Sapphire

by Nasrina Parvin Khan

A good Star Sapphire should be eye clean and have velvet like softness, as opposed to diamond like transparency.

INTRODUCTION OF STAR SAPPHIRE

Sapphire- the heavenly stone of this Earth is one of the most precious stone among the gems.

Sapphire is the single crystal form of Aluminium oxide (Al2O3), a mineral known as corundum. The heat and the pressure depths of the ground help the pure Aluminium oxide to crystallize into beautiful and splendid white gemstone since the age. Small amounts of other elements such as chrome and iron are the reason to turned this white crystal into colorful. Sapphires available in sky blues or sunset colors. The color of sapphires may be blue, red, yellow, pink purple, orange or greenish color.

Rubies are also part of corundum group. There was a debate which stone may be termed as a sapphire for long years. Finally it was decided that ruby-red sapphires would be “Rubies” and all other colors would be “Sapphires”.

Though sapphires are available in various colors, but the most popular color of sapphires is blue.

When we talk about sapphires, most people will think about blue. Sapphires other than blue are known as ‘fancy’. So fancy sapphires referred to yellow, pink, purple, green, black or white sapphires.

The most important characteristic of sapphires is its excellent hardness. Moh’s scale shows the hardness grade 9. The hardness of sapphire placed with ruby just after the diamond. Sapphires are easy to care and handle because of their great hardness.

Usually sapphire occurs in sedimentary limestone, metamorphic marble, and igneous basalt, pegmatite or andesine dikes. Naturally corundum mined from secondary alluvial deposits and rarely from primary deposits.

There are various kinds of sapphires, like- “Blue sapphires”, “Fancy sapphires”, “Padparadsha”, (means lotus flower)-an orange color variety of sapphires with a fine pinkish undertone and very unique “Star Sapphire”.

BLUE SAPPHIRES

The main color of sapphires is blue. It is the most popular color of sapphires also. In the ancient time, every blue gem material was called sapphire. As for example we can say the name of Lapis lazuli. So, the name “Sapphire” derives from the Greek word ‘Sappheiros’, which means blue.

Blue is the most desired color of sapphires. This gems available in all the shades of blue skies, from the deep blue of evening skies to the bright and deep blue of a clear and wonderful summer sky. Blue fascinates all the people. Actually blue is the favorite color of about 50 per cent of the population in this World. This color has a strong association with emotions such as sympathy and harmony, friendship and loyalty. These emotions represent anything permanent and reliable. So, the sapphire blue has become the color of permanent and reliable things. Thus the women in many countries decide on sapphire for their engagement rings.

STAR SAPPHIRE

Most of the blue sapphires are found in the form star sapphires. Star sapphire is a variety of sapphire that shows a star like special optical phenomenon named as “asterism”.

It is a rare variety of sapphires. Nearly 3 stars are discovered in every 100 faceted corundum mined. Though Star Sapphires are more common than the Star Ruby. But finer colored stone with fine star is very rare. Except blue, star sapphire is also available in black.

“Asterism” is a phenomenon by which a star shaped light effect has been shown across the surface of the gem through the reflection or transmission of light.

Star Sapphire is one of the most popular star gems, which shows an illuminated, wavy star bellow the surface of the crystal.

Usually Star Sapphire shows the six legged star effect. But it can shows four to twelve rays depending on the crystal system of the gems. Twelve rays star effect in sapphire is very occasional.

WHAT CAUSES STAR EFFECT

Star effect or “asterism” is caused by the dense inclusions of tiny fibers of foreign particles in gems. Generally, these inclusions are the reason of the reflection of light and form a wavy star like formation, which moves around when the mineral is rotated. All the inclusions in the gem are form via exsolution.

Solid crystal inclusions found within the corundum sapphire. Some sapphires leave holes or empty areas in the host, which filled with liquid, gas or solid. Reflection creates from fibers or fibrous cavity in the crystal.

The inclusions must be long, very thin needle like which called as ‘rutile’. “Asterism” is produced when the light is concentrate into 3 rays that intersects at right angles to the direction of the needles. Thus we get a six-rayed star. Small needles of rutile sometimes called ‘silk’ are oriented inside the minerals in the direction of the crystal growth system. There is relationship between the gem’s growth and the number of rays produced by the reflected light.

The arrangements of needles in a hexagonal pattern produced six-rayed ‘asterism’.

Exsolved inclusions form a pattern in the host mineral to form a star. This pattern remains same in case of sapphire. The rays of star should cross at the top of the sapphire and must be distinct.

QUALITY OF A STAR

The sharpness and the size of the star in sapphire depend on the quality and quantity of rutile needles. We get a better star in sapphire when the rutile packed more densely. Longer needles also produce a better star than the tiny particles. When the quantities of needles are much more, sapphire turned into a low translucent stone and lack ‘asterism’. It also harms the color of sapphire.

CUTTING OF A STAR SAPPHIRE

Cutting is very important to exhibit the star effect in sapphire. Proper cutting helps to extracts the beauty of the gem. To display the star effect in best way, a sapphire must be cut as cabochon with the girdle, parallel to the needles. Medium to high cabochons need to be cut to get a perfect star in sapphire. The domed must be round or oval shaped.

COLOR OF STAR SAPPHIRE

Generally Star Sapphires are available in blue. But other colors can also be seen. The color of ruby is red. Star Sapphires are also available in black, purple, and grey and so on. Varieties of blue colored Star Sapphires are found. Star Sapphires from Sri Lanka are light blue or grey.

VALUE OF STAR SAPPHIRE

The carat weight is not the only factor that decides the value of a star sapphire. It also depends on the body color, intensity and the visibility of the star as well as the strength and sharpness of the star. All six legs of the star should be straight and prominent.

Heat treatment is always used to produce, intensify or lighten color or improves color uniformity and appearance of blue sapphire. But some people preferred untreated, natural stone.

A good Star Sapphire should be eye clean and have velvet like softness, as opposed to diamond like transparency.

The market value of a sapphire is also depends on its origin. Sapphires mined from Sri Lanka are the most valuable.

OCCURRENCE OF STAR SAPPHIRE

Finer qualities Star Sapphires are found in Myanmar (Burma), Thailand, India, Sri Lanka, Tanzania, Afghanistan, Brazil, Cambodia, Malagasy Republic, Malawi, Pakistan, Rhodesia of Zimbabwe and Montana and North Carolina of US. But the best quality Star Sapphires are available in Sri Lanka.

FAMOUS STAR SAPPHIRE

The most famous and largest cut star sapphire is 543-carat “Star of India“. The “Mid night Star”- a black sapphire is also famous one. Both of these Star Sapphires are housed at the American Museum of Natural History in New York City. 330-carat “Star of Asia” at the Smithsonian is another famous Star Sapphire in the world..