Sapphire

 

In earlier times, some people believed that the firmament was an enormous blue sapphire in which the Earth was embedded. Could there be a more apt image to describe the beauty of an immaculate sapphire? And yet this gem comes not in one but in all the blue shades of that firmament, from the deep blue of the evening sky to the shining mid-blue of a lovely summer's day which casts its spell over us. However, this magnificent gemstone also comes in many other colours: not only in the transparent greyish-blue of a distant horizon but also in the gloriously colourful play of light in a sunset – in yellow, pink, orange and purple. Sapphires really are gems of the sky, although they are found in the hard ground of our 'blue planet'. 

 

 

Blue is the main colour of the sapphire. Blue is also the favourite colour of some 50 per cent of all people, men and women alike. We associate this colour, strongly linked to the sapphire as it is, with feelings of sympathy and harmony, friendship and loyalty: feelings which belong to qualities that prove their worth in the long term – feelings in which it is not so much effervescent passion that is to the fore, but rather composure, mutual understanding and indestructible trust. Thus the blue of the sapphire has become a colour which fits in with everything that is constant and reliable. That is one of the reasons why women in many countries wish for a sapphire ring on their engagement. The sapphire symbolises loyalty, but at the same time it gives expression to people's love and longing. Perhaps the most famous example of this blue is to be found in music, in George Gershwin's "Rhapsody in Blue". And the blue of the sapphire even appears where nothing at all counts except clear-sightedness and concentrated mental effort. The first computer which succeeded in defeating a world chess champion bore the remarkable name 'Deep Blue'.

  

 

What makes the sapphire so fancy?

Its beauty, its magnificent colours, its transparency, but also its constancy and durability are qualities associated with this gemstone by gemstone lovers and specialists alike. (This does not only apply to the blue sapphire, but more of that later on). The sapphire belongs to the corundum group, the members of which are characterised by their excellent hardness (9 on the Mohs scale). Indeed their hardness is exceeded only by that of the diamond – and the diamond is the hardest mineral on Earth! Thanks to that hardness, sapphires are easy to look after, requiring no more than the usual care on the part of the wearer.

  

The gemstones in the corundum group consist of pure aluminium oxide which crystallised into wonderful gemstones a long time ago as a result of pressure and heat at a great depth. The presence of small amounts of other elements, especially iron and chrome, are responsible for the colouring, turning a crystal that was basically white into a blue, red, yellow, pink or greenish sapphire. However, this does not mean that every corundum is also a sapphire. For centuries there were differences of opinion among the specialists as to which stones deserved to be called sapphires. Finally, it was agreed that the ruby-red ones, coloured by chrome, should be called 'rubies' and all those which were not ruby-red 'sapphires'.

  

 

If there is talk of the sapphire, most gemstone aficionados think immediately of a velvety blue. It's a versatile colour that becomes many wearers. A blue sapphire fits in best with a well balanced lifestyle in which reliability and temperament run together and there is always a readiness to encounter things new – as with the woman who wears it. The fact that this magnificent gemstone also comes in a large number of other colours was known for a long time almost only to insiders. In the trade, sapphires which are not blue are referred to as 'fancies'. In order to make it easier to differentiate between them, they are referred to not only by their gemstone name but also by a description of their colour. In other words, fancy sapphires are described as yellow, purple, pink, green or white sapphires. Fancy sapphires are pure individualism and are just made for lovers of individualistic coloured stone jewellery. They are currently available in a positively enchanting variety of designs - as ring stones, necklace pendants or ear jewellery, as solitaires, strung elegantly together or as sparkling pavée.

  

 

However, the sapphire has yet more surprises in store. For example there is an orange variety with a fine pink undertone which bears the poetic name 'padparadscha', which means something like 'lotus flower'. The star sapphires are another rarity, half-dome-cut sapphires with a starlike light effect which seems to glide across the surface of the stone when it is moved. There are said to have been gemstone lovers who fell in love with these sapphire rarities for all time. And indeed the permanence of relationships is one of the features that are said to belong to this gemstone.

   

Top-quality sapphires are rare

Sapphires, call them gemstones of the sky though we may, lie well hidden in just a few places, and first have to be brought to light through hard work. Sapphires are found in India, Burma, Ceylon, Thailand, Vietnam, Australia, Brazil and Africa. From the gemstone mines, the raw crystals are first taken to the cutting-centres where they are turned into sparkling gemstones by skilled hands. When cutting a sapphire, indeed, the cutter has to muster all his skill, for these gemstones are not only hard. Depending on the angle from which you look at them they also have different colours and intensities of colour. So it is the job of the cutter to orientate the raw crystals in such a way that the colour is brought out to its best advantage.

Depending on where they were found, the colour intensity and hue of the cut stones vary, which means, later on, that the wearer is rather spoilt for choice. Should she perhaps go for a mid-blue stone which will remind her even on rainy days of that shining summer sky? Or should she prefer a lighter blue because it will continue to sparkle vivaciously when evening falls? The bright light of day makes most sapphires shine more vividly than the more subdued artificial light of evening. So in fact it is not, as is often claimed, the darkest tone that is the most coveted colour of the blue sapphire, but an intense, rich, full blue which still looks blue in poor artificial light.

Specialists and connoisseurs regard the Kashmir colour with its velvety shine as the most beautiful and most valuable blue. These magnificent gemstones from Kashmir, found in 1880 after a landslide at an altitude of 16,000 feet and mined intensively over a period of eight years, were to have a lasting influence on people's idea of the colour of a first-class sapphire. Typical of the Kashmir colour is a pure, intense blue with a very subtle violet undertone, which is intensified yet more by a fine, silky shine. It is said that this hue does not change in artificial light. But the Burmese colour is also regarded as particularly valuable. It ranges from a rich, full royal blue to a deep cornflower blue.

  

 

The oldest sapphire finds are in Ceylon, or Sri Lanka as it is known today. There, people were already digging for gemstones in ancient times. The specialist recognises Ceylon sapphires by the luminosity of their light to mid-blue colours. Having said that, most blue sapphires come either from Australia or from Thailand.

Their value depends on their size, colour and transparency. With stones of very fine quality, these are, however, not the only main criteria, the origin of the gem also playing a major role. Neither is the colour itself necessarily a function of the geographical origin of a sapphire, which explains the great differences in price between the various qualities. The most valuable are genuine Kashmir stones. Burmese sapphires are valued almost as highly, and then come the sapphires from Ceylon. The possibility of the gemstone's having undergone some treatment or other is also a factor in determining the price, since gemstones which can be guaranteed untreated are becoming more and more sought-after in this age of gemstone cosmetics. And if the stone selected then also happens to be a genuine, certificated Kashmir or Burmese, the price will probably reflect the enthusiasm of the true gemstone lover.

 

 

It is not often that daring pioneers discover gemstones on a scale such as was the case on Madagascar a few years ago, when a gemstone deposit covering an area of several miles was found in the south-east of the island. Since then, not only have there been enough blue sapphires in the trade, but also some splendid pink and yellow sapphires of great beauty and transparency. Meanwhile, experts in Tanzania have also found initial evidence of two large-scale gemstone deposits in the form of some good, if not very large sapphire crystals coloured blue, green, yellow and orange. And the third country to register new finds recently was Brazil, where sapphires ranging from blue to purple and pink have been discovered. So lovers of the sapphire need not worry: there will, in future, be enough of these 'heavenly' gems with the fine colour spectrum. Top-quality sapphires, however, remain extremely rare in all the gemstone mines of the world.

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  Sapphire (Greek: σάπφειρος; sappheiros "blue stone") is a gemstone variety of the mineral corundum, an aluminium oxide (α-Al2O3), when it is a color other than red or dark pink, in which case the gem would instead be called a ruby, considered to be a different gemstone. Trace amounts of other elements such as iron, titanium, or chromium can give corundum blue, yellow, pink, purple, orange, or greenish color. Pink-orange sapphires are also called padparadscha. Pure chromium is the distinct impurity of rubies. However, a combination of e.g. chromium and titanium can give a sapphire of a color distinct from red.
Sapphires are commonly worn as jewellery. Sapphires can be found naturally, by searching through certain sediments or rock formations, or they can be manufactured for industrial or decorative purposes in large crystal boules. Because of the remarkable hardness of sapphires (and of aluminum oxide in general), sapphires are used in some non-ornamental applications, including infrared optical components, such as in scientific instruments; small, high-durability windows (also used in scientific instruments); wristwatch crystals; and very thin electronic wafers, which are used as the insulating substrates of very special-purpose solid-state electronics (most of which are integrated circuits).

Natural sapphires

The sapphire is one of the two or three gem-varieties of corundum, with another one being the red or deep pink ruby. Although blue is their most well-known hue, sapphires are made up of any color of corundum except for red (red ones are called rubies). Sapphires may also be colorless, and they are also found in shades of gray and black.

  

 

The cost of natural sapphires varies depending on their color, clarity, size, cut, and overall quality - as well as their geographic origin, oddly enough. Significant sapphire deposits are found in Eastern Australia, Thailand, Sri Lanka, Madagascar, East Africa, and in North America in a few locations, such as at "Gem Mountain", and in or near the Missouri River in the region around Helena, Montana. Sapphire and rubies are often found together in the same area, but one gem is usually more abundant.

Blue sapphire

Color in gemstones breaks down into three components: hue, saturation, and tone. Hue is most commonly understood as the "color" of the gemstone. Saturation refers to the vividness or brightness or "colorfulness" of the hue, and tone is the lightness to darkness of the hue. Blue sapphire exists in various mixtures of its primary (blue) and secondary hues, various tonal levels (shades) and at various levels of saturation (brightness).

  

 

Blue sapphires are evaluated based upon the purity of their primary hue. Purple, violet, and green are the most common secondary hues found in blue sapphires. Violet and purple can contribute to the overall beauty of the color, while green is considered to be distinctly negative. Blue sapphires with up to 15% violet or purple are generally said to be of fine quality. Blue sapphires with any amount of green as a secondary hue are not considered to be fine quality. Gray is the normal saturation modifier or mask found in blue sapphires. Gray reduces the saturation or brightness of the hue and therefore has a distinctly negative effect.

The color of fine blue sapphires can be described as a vivid medium dark violet to purplish blue where the primary blue hue is at least 85% and the secondary hue no more than 15% without the least admixture of a green secondary hue or a gray mask.

The 423 carats (85 g) Logan sapphire in the National Museum of Natural History, in Washington, D.C., is one of the largest faceted gem-quality blue sapphires in existence.

Fancy color sapphire

Yellow and green sapphires are also commonly found. Pink sapphires deepen in color as the quantity of chromium increases. The deeper the pink color the higher their monetary value as long as the color is trending towards the red of rubies.

  

 

Sapphires also occur in shades of orange and brown, and colorless sapphires are sometimes used as diamond substitutes in jewelry. Padparadscha sapphires often draw higher prices than many of even the finest blue sapphires. Recently, more sapphires of this color have appeared on the market as a result of a new artificial treatment method that is called "lattice diffusion".

Padparadscha

Padparadscha is a pink-orange corundum, with a low to medium saturation and light tone, originally being mined in Sri Lanka, but also found in deposits in Vietnam and Africa; Padparadscha sapphires are very rare and highly valued. The name derives from the Sinhalese word for lotus blossom. 

   

Along with rubies, they are the only type of corundum to be given their own name instead of being called a particular colored sapphire. Padparadscha used to be a subvariety of ruby. The rarest of all padparadschas is the totally natural variety, with no sign of treatment.

Star sapphire

A star sapphire is a type of sapphire that exhibits a star-like phenomenon known as asterism. Star sapphires contain intersecting needle-like inclusions (often the mineral rutile, a mineral composed primarily of titanium dioxide) that cause the appearance of a six-rayed "star"-shaped pattern when viewed with a single overhead light source.

 

  

The Black Star of Queensland is believed to be the largest star sapphire that has ever been mined, and it weighs 733 carats. The Star of India (weighing 563.4 carats) is thought to be the second-largest star sapphire, and it is currently on display at the American Museum of Natural History in New York City. The 182-carat Star of Bombay, located in the National Museum of Natural History, in Washington, D.C., is an example of a blue star sapphire.

   

The value of a star sapphire, however, depends not only on the weight of the stone but also the body color, visibility and intensity of the asterism.

Color change sapphire

A rare variety of sapphire, known as color change sapphire, exhibits different colors in different light. Color change sapphires are blue in outdoor light and purple under incandescent indoor light; they may also be pink in daylight to greenish under fluorescent light. Some stones shift color well and others only partially, in that some stones go from blue to bluish purple. While color change sapphires come from a variety of locations, the gem gravels of Tanzania is the main source.

Certain synthetic color-change sapphires are sold as “lab” or “synthetic” alexandrite, which is accurately called an alexandrite simulant (also called alexandrium) since the latter is actually a type of chrysoberyl—an entirely different substance whose pleochroism is different and much more pronounced than color-change corundum (sapphire).

Source of color

Red rubies are corundum which contain chromium impurities that absorb yellow-green light and result in deeper ruby red color with increasing content. Purple sapphires contain trace amounts of vanadium and come in a variety of shades. Corundum that contains ~0.01% of titanium is colorless. If trace amounts of iron are present, a very pale yellow to green color may be seen. If both titanium and iron impurities are present together, however, the result is a magnificent deep-blue color.

Unlike localized ("interatomic") absorption of light which causes color for chromium and vanadium impurities, blue color in sapphires comes from intervalence charge transfer, which is the transfer of an electron from one transition-metal ion to another via the conduction or valence band. The iron can take the form Fe2+ or Fe3+, while titanium generally takes the form Ti4+. If Fe2+ and Ti4+ ions are substituted for Al3+, localized areas of charge imbalance are created. An electron transfer from Fe2+ and Ti4+ can cause a change in the valence state of both. Because of the valence change there is a specific change in energy for the electron, and electromagnetic energy is absorbed. The wavelength of the energy absorbed corresponds to yellow light. When this light is subtracted from incident white light, the complementary color blue results. Sometimes when atomic spacing is different in different directions there is resulting blue-green dichroism.

   

Intervalence charge transfer is a process that produces a strong colored appearance at a low percentage of impurity. While at least 1% chromium must be present in corundum before the deep red ruby color is seen, sapphire blue is apparent with the presence of only 0.01% of titanium and iron.

Treatments

Sapphires may be treated by several methods to enhance and improve their clarity and color. It is common practice to heat natural sapphires to improve or enhance color. This is done by heating the sapphires in air to temperatures between 500 and 1800 °C for several hours, or by heating in a nitrogen-deficient atmosphere oven for seven days or more. Upon heating, the stone becomes a more blue in color but loses some of the rutile inclusions (silk). When high heat temperatures are used, the stone loses all of the silk and becomes clear under magnification. Evidence of sapphire and other gemstones being subjected to heating goes back to, at least, Roman times. Un-heated stones are quite rare and will often be sold accompanied by a certificate from an independent gemological laboratory attesting to "no evidence of heat treatment".

  

 

Diffusion treatments are somewhat more controversial as they are used to add elements to the sapphire for the purpose of improving colors. Typically beryllium is diffused into a sapphire with very high heat, just below the melting point of the sapphire. Initially (c. 2000) orange sapphires were created with this process, although now the process has been advanced and many colors of sapphire are often treated with beryllium. It is unethical to sell beryllium-treated sapphires without disclosure, and the price should be much lower than a natural gem or one that has been enhanced by heat alone.

Treating stones with surface diffusion is generally frowned upon because when stones chip or are repolished/refaceted the 'padparadscha' colored layer can be removed. (There are some diffusion treated stones in which the color goes much deeper than the surface, however.) The problem lies in the fact that treated padparadschas are at times very difficult to detect, and they are the reason that getting a certificate from a reputable gemological lab (e.g., Gubelin, SSEF, AGTA, etc.) is recommended before investing in them.

According to Federal Trade Commission guidelines, in the United States, disclosure is required of any mode of enhancement that has a significant effect on the gem's value.

Mining

Sapphires are mined from alluvial deposits or from primary underground workings. The mining locations include Myanmar, Madagascar, Sri Lanka, Australia, Thailand, India, Pakistan, Afghanistan, Tanzania, Kenya, and China. The Logan sapphire, the Star of India, and the Star of Bombay originate from Sri Lankan mines.

   

  

Madagascar is the world leader in sapphire production (as of 2007) specifically its deposits in and around the city of Ilakaka. Prior to the opening of the Ilakaka mines, Australia was the largest producer of sapphires (such as in 1987). In 1991, a new source of sapphires was discovered in Andranondambo, southern Madagascar. That area has been exploited for its sapphires started in 1993, but it was practically abandoned just a few years later - because of the difficulties in recovering sapphires in their bedrock. This kind of sapphire has been sold as the "Kashmir sapphire" in international markets.

In North America, sapphires have been mined mostly from deposits around Helena, Montana. A few gem-grade sapphires and rubies have also been found in the area of Franklin, N.C.

Synthetic sapphire

In 1902, the French chemist Auguste Verneuil developed a process for producing synthetic sapphire crystals. In the Verneuil process, named for him, fine alumina powder is added to an oxyhydrogen flame, and this is directed downward against a mantle. The alumina in the flame is slowly deposited, creating a teardrop shaped "boule" of sapphire material. Chemical dopants can be added to create artificial versions of the ruby, and all the other natural colors of sapphire, and in addition, other colors never seen in geology. Artificial sapphire material is identical to natural sapphire, except it can be made without the flaws that are found in natural stones. The disadvantage of Verneuil process is that the grown crystals have high internal strains. Many methods of manufacturing sapphire today are variations of the Czochralski process, which was invented in 1916. In this process, a tiny sapphire seed crystal is dipped into a crucible made of the precious metal rhodium, containing molten alumina, and them slowly withdrawn upward at a rate of one to 100 mm per hour. The alumina crystallizes on the end, creating long carrot-shaped boules of large size, up to 400 mm in diameter and weighing almost 500 kg.

  

 

In 2003, the world's production of synthetic sapphire was 250 tons (1.25 × 109 carats), mostly by the United States and Russia. The availability of cheap synthetic sapphire unlocked many industrial uses for this unique material:

The first laser was made with a rod of synthetic ruby. Titanium-sapphire lasers are popular due to their relatively rare capacity to be tuned to various wavelengths in the red and near-infrared region of the electromagnetic spectrum. They can also be easily mode-locked. In these lasers, a synthetically-produced sapphire crystal with chromium or titanium impurities is irradiated with intense light from a special lamp, or another laser, to create stimulated emission.

One application of synthetic sapphire is sapphire glass. Here glass is a layman term which refers not to the amorphous state, but to the transparency. Sapphire is not only highly transparent to wavelengths of light between 170 nm and 5.3 μm (the human eye can discern wavelengths from about 380 nm to 750 nm), but it is also five times stronger than glass and ranks a 9 on the Mohs Scale, and much tougher than tempered glass although not as much as synthetic stabilized zirconium oxide (such as yttria-stabilized zirconia). Along with zirconia and aluminium oxynitride, synthetic sapphire is used for shatter resistant windows in armored vehicles and various military body armor suits, in association with composites. Sapphire "glass" (although being crystalline) is made from pure sapphire boules by slicing off and polishing thin wafers. Sapphire glass windows are used in high pressure chambers for spectroscopy, crystals in high quality watches, and windows in grocery store barcode scanners since the material's exceptional hardness and toughness makes it very resistant to scratching.
Cermax xenon arc lamp with synthetic sapphire output window

Synthetic sapphire is industrially produced from agglomerated aluminum oxide, sintered and fused in an inert atmosphere (hot isostatic pressing for example), yielding a transparent polycrystalline product, slightly porous, or with more traditional methods such as Verneuil, Czochralski, flux method, etc., yielding a single crystal sapphire material which is non-porous and should be relieved of its internal stress.

One type of xenon arc lamp (originally called the "Cermax" its first brand name), which is now known generically as the "ceramic body xenon lamp", uses sapphire crystal output windows that tolerate higher thermal loads - and thus higher output powers when compared with conventional Xe lamps with pure silica window.

Thin sapphire wafers are also used as an insulating substrate in high-power, high-frequency CMOS integrated circuits. This type of IC is called a silicon on sapphire or "SOS" chip. These are especially useful for high-power radio-frequency (RF) applications such as those found in cellular telephones, police car and fire truck radios, and satellite communication systems. "SOS" allows for the monolithic integration of both digital and analog circuitry all on one IC chip.

The reason for choosing wafers of artificial sapphire, rather than some of other substance, for these subtrates is that sapphire has a quite low conductivity for electricity, but a much-higher conductivity for heat. Thus, sapphire provides good electrical insulation, while at the same time doing a good job at helping to conduct away the significant heat that is generated in all operating integrated circuits. Thus, the choice of sapphire material for these substrates was not an arbitrary one, but rather, it is a choice that is made for serious electronics engineering reasons.

Wafers of single-crystal sapphire material are also used in the semiconductor industry as a non-conducting substrate for the growth of devices based on gallium nitride (GaN). The use of the sapphire material significantly reduces the cost, because this has about one-seventh the cost of germanium. Gallium nitride on sapphire is commonly used in blue light-emitting diodes (LEDs).

Historical and cultural references

    * Some etymologists propose an old Sanskrit origin to the Semitic word "sappir": a dark colored precious stone called "Shanipriya" (शनिप्रिय), from "shani" (शनि) meaning "Saturn" and "priya" (प्रिय), precious, i.e. "precious to Saturn".

    * According to Rebbenu Bachya, and in many English Bible translations, the word "Sapir" in the verse Exodus 28:18 means "sapphire" and was the stone on the Ephod representing the tribe of Issachar. However, it has been suggested that the English word "sapphire" stems from the Hebrew word "sapir" (ספיר) (via the Greek word "sapphiros"; σάπφειρος). Sapphires were actually not known as a distinct stone before the time of the Roman Empire. They were earlier considered to be forms of the mineral jacinth, rather than needing a word of their own. Prior to the time of the Roman Empire, "sapphiros" referred to any blue gem in general.

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