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..

Synthetic sapphires

by Ardamun Ramdeva

Having identical chemical composition and physical properties of natural sapphires, synthetic sapphires, over the years, have achieved a high degree of perfection. The many different methods of producing synthetic sapphires are: melt growth, solution growth, or extremely high-temperature, high-pressure growth processes.

Synthetic Sapphires – Gemstones Par Excellence

Sapphire was first synthesized in 1902. Synthetic Ruby – the ‘red sapphire’, though, was produced in 1888 by the French chemist, Auguste Victor Louis Verneuil, through flame fusion process. A synthetic sapphire or the one created in a lab, under controlled conditions, has crystal structure, optical properties and chemical composition of its natural avatar. Some synthetic processes simulate the geological conditions required to produce natural sapphire. Both, Sapphire and Ruby, are varieties of corundum, a crystalline form of aluminum oxide. In nature, corundum comes in various shades of blue, as well as colorless, red, yellow, pink, orange, brown, purple, and green. Corundum of all colors is known as Sapphire, except the red sapphire, which is known as Ruby.

The word sapphire is known to originate from the Latin ‘sapphärus’, Middle English ‘saphir’, Old French ‘safir’, Greek ‘sappheiros’, and Hebrew ‘sappîr’.

Production of Synthetic Sapphires

Synthetic sapphires come in almost all colors, but the most sought after is the deep blue sapphire. Basically, to get different colors, dopants are added to aluminum oxide. Sapphires are synthesized by melting these at over 2000º Celsius. Having identical chemical composition and physical properties of natural sapphires, synthetic sapphires, over the years, have achieved a high degree of perfection. The many different methods of producing synthetic sapphires are: melt growth, solution growth, or extremely high-temperature, high-pressure growth processes.

The flame fusion process of Auguste Verneuil involves producing a boule from finely ground form of aluminum oxide, or Alumna, with the help of an inverted oxyhydrogen torch. Boule is a mass of alumna with the same physical and chemical properties of corundum. Oxygen passes through a chamber containing highly purified alumna, and this is carried to the central part of the oxyhydrogen flame. The fine alumna particles fuse and fall down as molten boule. Flame, rate of the feed of alumna, and the lowering of boule are controlled and adjusted to produce a boule of uniform size and shape. To produce colorless sapphire, the melting point of boule is 2030º Celsius. The furnace is shut down once the boule reaches the desired size of 150 or 200 carats, and is allowed to cool.

The Kyropoulos method of producing synthetic sapphires involves growing sapphire crystals under controlled conditions. During the process of crystallization, sapphire crystals sprout in cylindrical shapes. The required diameter of the crystal is maintained by the automatic displacement of the seed crystal, without rotation. The melt is achieved through resistive heating. The Kyropoulos method produces sapphire with minimal mechanical stress.

The Czochralski (pulling) process involves melting the powdered ingredients in a platinum, iridium, graphite, or ceramic crucible. A rotating rod, with a seed crystal attached to one end, is lowered to touch the melt. The rod is slowly withdrawn at the rate of 1 to 100 millimeters (mm) per hour. As the seed pulls the material from the melt, it cools and solidifies. Very high purity large crystals of more than 50 mm in diameter and 1 meter in length are grown by this method.

Some of the other processes for producing synthetic sapphires are: the floating zone process, the flux process, and the hydrothermal process.

Uses of Synthetic Sapphires

There are many uses of synthetic sapphires – as gemstone, as well as non-gemstone. Sharing the physical, chemical and optical qualities and properties of the natural sapphire, the synthetic sapphires are used extensively in jewelry. Some of the synthetic sapphires are so perfect that it becomes difficult to identify them, unless by an experienced jeweler or a gemologist. Padparadscha sapphires are rare orange-pink variety of sapphires and have a higher value than even the blue sapphires. These sapphires have been created in labs. They are so perfect that a few years ago, the synthetic Padparadscha sapphires were rated as natural till the American Gem Trade Association (AGTA) found out they were not so.

Jewelry produced by synthetic sapphires is just as beautiful as the one by natural sapphires. Though not inexpensive, synthetic sapphire jewelry costs less than that of natural sapphire. Synthetic sapphires range in price and size, and the smaller sapphires are used in less expensive jewelry. As a matter of ethics, the origin of the sapphire should always be disclosed. Though synthetic sapphires can technically be called ‘genuine’, they are certainly not natural. One should learn about synthetic sapphires before buying jewelry, to know what one is buying.

Other applications of synthetic sapphires include their use in watch and semi-conductor industries. It was first used as watch crystals in the 1960s. It is used in most high-end watch brands. Synthetic sapphire crystals are grown in cylindrical ingots. These ingots of pure synthetic sapphires are sliced into wafers. These are polished into transparent crystal slices. High quality watches use these slices as watch faces. The exceptional hardness of the material makes the watch face impossible to scratch.

Wafers of single crystal synthetic sapphires are used in semi-conductor industry for light emitting diodes. For its extreme abrasive resistance, synthetic sapphire is the jewel of choice. Its other features include, zero porosity, extreme hardness, low-friction coefficient, chemical inertness – even to hydrofluoric acid, high thermal conductivity, and excellent wear resistance. Due to zero porosity, micro-finishes of two can be attained.

Precision jeweled bearing rollers use sapphire balls for their low-friction and long-wear applications. Some advantages of using synthetic sapphires as jeweled bearings are:

* Low friction, hardness and shock resistance
* Close tolerances
* Accurate wear life
* Non magnetic properties
* Resistance to heat, corrosion, and distortion

Due to their high melting point of 2000º Celsius, they are suitable for high-heat applications also. The other uses of synthetic sapphires include electronics, optoelectronics, optics, and laser technologies.

Identification of Synthetic Sapphires

* Presence of round, elliptical or flask shaped bubbles.
* Whitish sheen seen in natural sapphires is missing in synthetics
* Strain cracks, curved striae (fine thread-line lines or streaks), wispy white veils, etc
* Flux inclusions and non-natural gas inclusions
* Visible seed crystals in synthetic sapphires
* Color zones seen when dipped in Methylene Iodide.
* Absorption spectra not seen in synthetic sapphires.
* Unnatural looking colors.
* Dark un-fused blotches seen. Caused by coloring matter.
* Variation in properties of fluorescence.
* Transparency to Ultra Violet light varies.
* Star effect in synthetic sapphires seems to be painted.
* The synthetics have a neatly ground out base as against the lumpy base of natural sapphires.

Important Sapphire Mines In The World

by Ritika Changrani

Sapphires are beautiful stones found in myriad colors like blue, yellow, orange, purple and even pink. The most expensive sapphires are not those which have been heat treated but those which have been mined as nature intended them to be – straight from the depths of the earth. These are the rich & vibrant blue sapphires. Sapphires are mined all over the world. There are sapphire mines in India, Ceylon, Burma, Australia, Brazil, Thailand, Vietnam, USA, and Africa.

Sapphires are beautiful stones found in myriad colors like blue, yellow, orange, purple and even pink. The most expensive sapphires are not those which have been heat treated but those which have been mined as nature intended them to be – straight from the depths of the earth. These are the rich & vibrant blue sapphires.

Cutting a sapphire is difficult as a sapphire has many colors and a cutter faces the dilemma of trying to get the best in brilliance, depth of color and line while cutting the gems. A sapphire is valued depending on its size or carat, the color, clarity and the cut, or which we know and refer to as the Four Cs.

The chemical composition of the sapphire is dialuminum trioxide (Al₂O₃) which is a colorless and clear mineral. The stones get their color from the impurities that are present within it. For example, yellow comes from the iron so yellow plus titanium becomes blue and the red comes from chromium. Red sapphires are what the world knows as rubies. Titanium oxide is the most commonly found impurity which looks like silk needles. This is where the above mentioned heat treating comes into play. If the stone is treated to a heat reading 1700-2000 degrees Centigrade, the needles dissolve, the haze in the gem clears and the gem then acquires a brilliant look.

Sapphires are mined all over the world. You will find sapphires in India, Ceylon, Burma, Australia, Brazil, Thailand, Vietnam, USA, and Africa. The sad part is that the best sapphires are found in the strife ridden areas on the India – Pakistan border where the political situation is not one to be stepped into lightly. The Kashmir stones are the most valuable sapphires. The oldest mines are in Sri Lanka but the blue sapphires are mostly from Australia and Thailand. Madagascar will give you superb pinks and yellows and of course blue. Brazil has pink, purple and blue stones while in Tanzania you will find yellow, orange and blue.

The Aussie sapphire

The mine is at Reddestone Creek in Australia and this mine has seen plenty of mining over the last so many years. Mining right in the path of the stream is not allowed anymore since this was affecting the quality of the water. The commercial aspect of the Aussie sapphire commenced sometime in 1998.

Madagascar

Ilakaka and Sakaraha are situated a little south of the island Madagascar near a place called Toliara or Tulear. Since its discovery in 1998, the mine has seen active mining and trading from all over Madagascar is conducted here. Go past the desert southwards and you will reach a place called Andranondambo. Known at one time as Fort Dauphin, Tolanaro is a metasomatic sapphire mining area for blue sapphires where, in 1994 the first sapphires of gem quality were found.

Spokane Bar

Along the Missouri river on the banks of Hauser Lake, lies the Spokane gravel bar. It was named by geologists who were mapping the area in early 1900’s and they came upon a sapphire cache. Hauser was one of the territorial governors of Montana and the lake is named after him. This lake has played a very important role in the history of sapphire mining. The story goes that the governor and his partners were panning for gold. The sluice boxes got blocked by some heavy stones so the miners sent it to England where it was confirmed that these are sapphires and quite priceless. Today sapphires of every color and hue can be found at Spokane bar. Most common among these are the blue/green sapphires.

North Carolina

The Old Presley Sapphire Mine is situated near Canton in North Carolina in Haywood County. In western North Carolina this is the oldest mine in operation and its claim to fame is the discovery of 1445 carat sapphire which was called the Star of the Carolinas. Now the mine has plenty of moonstones, sapphires and various other precious stones waiting to be found.

Montana

In Montana the first mined Sapphires were found at the Rock Creek deposit around 1892. Earlier it was abundant in sapphires and today is noted as the only place that has quantities enough to make it a commercial venue for sapphires. Mining for gems is an activity that has been enjoyed by visitors and even Montanans themselves these days. Rock creek is the only one out of the four areas of sapphire deposits in Montana where the gem has such a fine quality and a variety of sharp colors. With brilliant jewelry being the preferred type among people, the Rock Creek sapphire has found its own niche market. With heat treatment also easily done, this industry has really taken hold. The other sapphire deposit region of Montana is Philipsburg. At the Sapphire Mountain and at Gem Mountain, mining is open to the public. This is a popular destination for sapphire mining and hunting.

Sri Lanka

Mining on the island of Sri Lanka goes back at least 2000 years. This island has its own heritage in the mining arena. The island is called Gem Island or “Ratna Dweepa” because of the large variety of gems found here. You will find everything from peridot to moonstones to garnets and topaz. Today Sri Lanka is best recognized for it’s the sapphires called the Ceylon Blue, and the sapphire called Padparadscha which has a beautiful and unique orange pink pastel soft color, very similar to the Lotus flower found on this island. The traditional Ceylon mines are near Ratnapura which is located southeast of Colombo about 100kms away.

Sapphires are found everywhere in the world. This stone has numerous astrological aspects to it also. There are varying opinions about its use and wearing it is considered beneficial for some while it is known to bring bad luck to others. But superstitions not withstanding, the blue sapphire is a beautiful stone with brilliance few can match.

Lab identification of Sapphire

by Erum Qureshi

Sapphire, derived from the Greek word sapphirus, literally means blue. Many people will find it difficult to believe that ruby, with its intense red color and the royal blue sapphire are the same mineral corundum composed of oxygen and the light metal aluminium.

Ideal sapphires are stones of an intense blue verging on the violet. Large sapphires are more common than large rubies. Let us look at the physical properties of the mineral species corundum to which the sapphire belongs.

Species

Metallic oxides are responsible for imparting color to this mineral. If not for these impurities present in the crystal structure of corundum, it would be colorless. Red stones of the corundum species are termed as rubies and all other colors are known as sapphires with the color prefix.

Corundum is found in many colors besides red and blue. Colorless Sapphire is called leuko-sapphire, yellow, violet, green and even brown colors may be found. Also sometimes found is a very rare and highly valued orange color, known as ‘padparadscha’ (from the Sinhalese word for ‘lotus flower’). Occasionally color-changing sapphires can be found; asterism and star-stones come in almost all colors.

Hardness

Hardness is the same as ruby (9 on the Moh’s scale) and also differs differently in different directions (an important factor which need to be kept in mind during cutting).

Determination of Specific Gravity

Specific gravity of a gemstone is the ratio of its weight to the same volume of water. Since there is no definite demarcation between ruby and sapphire, the same tests for measuring specific gravity are used as those for ruby. The Clerici solution is used to measure the specific gravity of sapphire as this solution is the heaviest among the high-density liquids available. The stone when suspended in the Clerici solution should be clean and dry as the tweezers and other apparatus used for the test. Care is should also be taken that these are free from other organic solutions before immersing the gem in the solution. Natural sapphire will have an SG approximating 3.99. An exception is iron-rich yellow, green and blue-green sapphires, which may have specific gravity as high as 4.00. Once the SG is confirmed to be that of corundum, the gemologist moves on to the next step.

Refractive Index

Light rays leaving one medium and entering another obliquely seem to bend a little at the place of contact. This is called refraction of light. During gem testing, measuring the refractive index or RI helps the gemologist observe the indices of refraction of light on a particular species of gemstone. The refractive index for sapphire is measured exactly in the same way as that of ruby, both being of the same species, their RI is the same. Spot readings are taken for cabochon cut sapphires; faceted stones are placed facedown on the glass of a Refractometer with a small amount of contact liquid and the reading is taken. The RI of sapphire will be 1.76 to 1.77.

Double Refraction

When a ray of light enters a crystal having a Trigonal system in directions other than the optic axis, it splits into two distinct rays. This is known as double refraction. The Sapphire, being of the Trigonal crystal structure shows two indices of refraction in a polariscope. These are known as the ordinary ray and the extraordinary ray. Birefringence is the difference between the highest and lowest refractive indices. Sapphire has a birefringence of – 0.008, with a negative sign because the ordinary ray is f greater value.

Pleochroism

The fact that there are two rays in these stones has an effect on color, for each of these rays absorbs light differently and as the stone is turned it shows a slightly different shade of color. This effect known as Dichroism, is seen fairly well in sapphires of all colors except in colorless and yellow stones. The most attractive color is that of the ordinary ray in sapphire, which is a deep royal blue.

Absorption Spectra

The absorption of colored stones is in well marked bands or finer dark lines which cross the otherwise continuous spectrum, obliterating certain colors or wavelengths when white light is transmitted through or reflected from the stone. The spectroscope is an instrument that determines the wavelength of the absorbed light. The wavelength is measured in nanometers (symbol nm) or angstrom symbol ?. The spectrum most common to blue, green and yellow Sapphire is the iron spectrum. It consists of three lines of increasing intensity at 451, 460 and 470 nm. The absorption spectra of sapphire (in nanometers):

Sapphire ,blue (from Australia) : 471, 460, 450.
Sapphire, blue (from Sri Lanka) : (450)

Note: Strong absorption lines are in bold letters; weak ones are in parenthesis.

Fluorescence

In the case of blue sapphires, UV fluorescence is practically non-existent. Except maybe Sri Lankan sapphires, which have chromium traces. These show a red or orange glow under long wave and weak blue glow under short wave.

Microscopic Examination

Without doubt the final and most determinative test to decide the authenticity of any gemstone is its examination under a microscope.

Gemologists rely on their expertise and experience to spot the inclusions before taking the final call on the authenticity and grade of a gemstone. The best stones are those with no major color zoning problems, which are well-cut, eye clean and most importantly of an intense blue color. Inclusions (irregularities in the crystal structure and internal flaws) in sapphire are straight angular growth lines following the crystal faces.

Included rutile needles or hematite plates are called ‘silk’, which bring about a soft sheen in the stone. When such a stone is cut en cabochon these rutile needles or ‘silk’ brings about the rare cat’s eye effect or the very desirable asterism (a six rayed star that shimmers above the stones surface when it is moved).

Rhombohedral twinning and boehmite needles are inclusions exclusive to natural corundum and have never been observed in flux grown synthetic corundums. Inclusions typical to synthetic sapphire are curved growth lines (thin striae or bands), gas bubbles and dense clouds of extremely fine rutile silk in star stones. These clouds do not show the straight angular zoning patterns that natural stones show but have curving bands instead.

Treatment and look-alikes

Through heat treatment at temperatures of about 1700-1800 degrees C, some cloudy sapphires, non-distinct in color, can change to a bright blue permanent color. Sapphires can be confused with benitoite, indicolite, iolite, spinel, tanzanite, topaz, zircon and even blue glass. Some imitations are made using doublets, blue cobalt glass with a crown of garnet or a crown of green sapphire and a pavilion of synthetic blue sapphire.

Today, synthetic sapphires having properties identical to the natural stone are being produced commercially.