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What color of sapphire is most valued?

Why is sapphire so valued? The main thing about the gemstone. Sapphire is a blue colored precious variety of corundum. A stone with a long history that has always attracted attention. It can be pure blue, or it can have shades of green or purple. Stones without additional shades are more valuable. In its pure form, corundum is colorless. The color depends on the admixtures of chemical elements. The stone has such a beautiful blue hue due to the presence of titanium and iron compounds. There are sapphires in other colors. They are usually called fantasy. There are yellow, orange, purple, pink, green, and colorless sapphires. But, it is important to note that blue sapphires belong to the group of precious stones according to the law of the Russian Federation. One of the important advantages of the mineral is its high hardness – 9 out of 10 on the Mohs scale.

  • Mineral: corundum
  • Chemical composition: Al2O3
  • Color: blue, violet blue, greenish blue
  • Optical character: anisotropic
  • Refractive index: 1,762 – 1,770 (+0,005; -0,003)
  • Birefringence: 0,008 – 0,010
  • Dispersion: 0,018
  • Shine: glass
  • Density: 4,00 g/cm 3 (+0,10; -0,05)
  • Hardness: 9

Place of Birth

The most beautiful and valuable are sapphires from a deposit in Kashmir (northern India). But, unfortunately, it has long been exhausted and was closed in 1928. Specimens once mined there are now collector’s items.

Beautiful specimens are mined in Sri Lanka, Madagascar, Burma, and Australia. Deposits in Thailand, Tanzania, and Cambodia are also rich in sapphires.

Deposit is an important factor influencing the cost of colored stones.

Characteristics of sapphire: color, clarity, weight and cut

A very important characteristic of sapphire. The most valuable are blue stones, without additional shades. There are a number of trade names for such stones in the international market, depending on their color. For example, royal sapphire – “Royal Blue” or “cornflower blue” – “Cornflower Blue”.

But there are also samples with shades of green or purple, which already reduce the cost of the stone. Very light or very dark (almost black) samples will also cost much less.

The purity of a stone is the presence or absence of various inclusions and cracks in it. The fewer inclusions, the higher its purity, the more transparent it is.

Sapphires are characterized by clusters of needle-shaped rutile crystals, which can create a “silky” effect, as well as the presence of crystals of other minerals and gas-liquid veils.

Inclusions in untreated sapphires: clusters of needle-shaped rutile inclusions (left and center), a veil of gas-liquid and crystalline inclusions (right)

The appearance of a sapphire can also be affected by color zoning – alternating dark and light stripes at an angle of 120 degrees or the distribution of color in the form of spots.

Color zoning (zonal clouds) in heat-treated sapphire

Weight and cut

The greater the weight of the stone, the more expensive it will be. Of course, taking into account the above important characteristics. Also, the cost of a sapphire can be affected by the proportionality of the cut.

Their beauty, manifestation of properties, color and purity depend on the quality of the cut. It is important that all proportions are maintained.

Ennobling

Ennobling – This is the artificial processing of stones in order to change their properties and appearance using various methods.

Sapphires are very often subjected to this method of refining: heat treatment.

First of all, in this way the color of the stone is changed. With the help of heating, the color can be made more saturated or, conversely, lightened, as well as get rid of additional shades.

The stones are heated in special furnaces to temperatures in the range of 800-1900°C, depending on the task.

Also, under the influence of temperature, some inclusions can dissolve, thus improving the purity of the stone.

Heat treatment is considered a classic refinement for sapphires, which is treated quite loyally.

Veils and rutile, melted after heat treatment

Veil melted after heat treatment

Another way to refine this mineral is diffusion treatment, which was developed back in the 1970s. During heat treatment, titanium oxide penetrates into the crystal lattice of the stone to create or enhance the blue color. Coloring occurs to a depth of no more than 1 mm, so the painted layer can easily come off when polishing the stone.

Visually, this processing method can be identified by clusters of a more saturated blue color on the edges of the stone and around cracks.

Later, already in the early 2000s, a technique was developed for coloring sapphires with another element – beryllium. The difference is that beryllium is a lighter element and can penetrate the entire depth of the stone. Diagnosing such samples is much more difficult.

Accumulations of a more saturated blue color on the edges of the stone and around cracks in diffusion-enhanced sapphire

Filling cracks and cavities with lead glass

This type of refining is used for sapphires much less frequently than for rubies, but such examples still occur.

Low quality stones with a lot of cracks are filled with a glassy compound to make them more transparent. This is mostly done before cutting.

Sapphires also undergo a heat treatment process at temperatures of around 1000°C.

The temperature is not too high, so the mineral inclusions generally retain their integrity.

Glass filler can be diagnosed based on certain characteristics. For example, by the presence of gas bubbles in cracks and so-called “flash effects” – blue, orange or purple reflections that are clearly visible when the stone is rocked.

Artificial sapphires

Artificial (synthetic) stone is artificially grown in laboratory conditions and is a complete analogue of natural stone.

Artificial sapphires are obtained using different methods. The first samples were obtained at the end of the 2000th – beginning of the XNUMXth century by the French scientist Auguste Verneuil by synthesis from melts. The process takes place at a very high temperature – about XNUMX°C. A special powder composition melts under the influence of temperature, then cools and crystallizes.

Most synthetic sapphires are obtained this way. Their main distinguishing feature is a clear curved (arc-shaped) color zoning – alternating light and dark stripes (in natural sapphires the zoning is located at an angle of 120°).

Two more popular methods for producing synthetic sapphires are: dissolving chemicals in molten flux (flux method) and dissolving substances in hot water at high pressure and temperature (hydrothermal method). Sapphires grown by the flux method are characterized by the presence of flux inclusions of various forms. Hydrothermal sapphires are characterized by uneven growth structures. By the way, growing sapphires using the hydrothermal method was developed by scientists from the Russian-Thai joint venture Tairus.

Simulations

Unlike synthetic analogues, imitations only repeat the appearance of the stone. Sapphire imitations may include other blue minerals (such as kyanite), glass, or composite stones. Samples consisting of two parts are called doublets, and samples of three are called triplets.

For many, the word “sapphire” is associated with the color blue. Blue is a kind of classic gemstone option. But depending on the presence of various impurities, crystals can take on completely different shades, from yellow to pinkish. Such colors are called fantasy.

Yellow

Homogeneous yellow minerals are very rare. Usually the color of the stone changes from pale yellow to rich amber, there are orange sapphires. In general, yellow species are quite rare in nature. They are mined in China, USA, Brazil, Thailand and Madagascar.

Blue

Blue is the most common color of sapphire. The most valuable are cornflower blue shades and the colors of a clear sky. Also appreciated are gems of a rich dark blue hue, but not quite dark. It is known that with the help of X-rays, the stone can be lightened.

The black

Black stones are usually opaque, but at the same time they have a bright sheen and iridescence in the facet area. The stone is considered a strong amulet. It is recommended to be worn by men and powerful women.

White

The white mineral or leucosapphire is comparable to a diamond. This is a completely transparent corundum, practically free of impurities in its composition. Natural white crystals are very rare in nature, they are usually obtained by heating colored corundums.

Blue

One of the most expensive shades of the gem. Almost all blue specimens were mined in India. Blue stones are recommended to be worn with caution. This is a very wayward mineral that suits rulers, sages and aesthetes. There is an opinion that the blue color reveals the ability to intuition and the gift of clairvoyance.

Green

In fact, the green hue is achieved by superimposing yellow and blue crystals, which can be seen in the structure of sapphire under a microscope. Green samples contribute to a healthy and restful sleep, help to remember dreams, which can be interpreted in the future.

Pink

Natural pink sapphires are very rare and comparable in price to pink diamonds. Known deposits of pink varieties in Madagascar and Sri Lanka. Sometimes sapphires of this shade are obtained by heating purple.

History and origin of the name

These super-strong transparent stones were first noticed by the Tamils ​​in Southeast Asia. They gave it the name corundum (translated as ruby). And the Greeks renamed it sapphire, which in their language means “blue gem”. Later we figured out the terminology. Red corundums remained rubies, while corundums of other colors remained sapphires. In Rus’ they were called azure yachts and were greatly revered.

Sapphire deposits and mining

Sapphires are mined in Thailand, Burma, Vietnam, China, India, Sri Lanka, and Madagascar. There are deposits on other continents (North America, Australia) in places of pegmatite deposits. In nature, the mineral is quite inconspicuous. In Russia, some corundum has been found on the Kola Peninsula and the Urals, but industrial mining is unprofitable.

The best is considered to be the Kashmir sapphire, which has a wonderful cornflower blue color. The deposit in Kashmir (Indian) is not currently being actively developed, so local sapphires are valued not only for their unique properties (the epithets alone are worth it: velvety, hazy, sleepy), but also for their exceptional rarity. Its color is considered the reference; all other shades are described in comparison with it. For example, Ceylon sapphire (Sri Lanka) is paler, and Burmese sapphire is darker than Kashmir sapphire. Sri Lanka supplies jewelers with the rare Padparadscha gem. Star-shaped specimens are also often found here.

Most blue corundum is mined in Thailand. The largest, brightest blue and purest sapphire, the “Jewel of the Jungle,” was discovered here. Its weight, according to the description, is 958 carats.

Physicochemical characteristics

The physical properties of sapphire can be the envy of any gemstone. Hardness on the Mohs scale – 9, density – 4 g/cm3, not brittle, very shiny. Composition: alumina, aluminum oxide. The chemical formula of sapphire is Al2O3. Pure corundum has no color; the blue color is given to it by metal impurities: iron, manganese, chromium, titanium. When heated, the color characteristics of the crystal change: pale ones become even lighter, dark ones turn pink. X-rays enhance the brightness of shades.

Why do sapphires come in different colors?

The chemical composition of the stone changes color. Corundum in its pure form is the element Al203. If it is truly pure, the result is a colorless gemstone or leucosapphire.

But often other things are thrown into the fray. Traces of elements such as iron, titanium and copper are often found. These elements may come and go in the form of stone. Their number affects the color. This is also why diamonds are sometimes blue (boron) or yellow (nitrogen).

How to distinguish from fakes

Natural sapphire stone is expensive and rare, so it is often counterfeited. In addition, methods for producing synthetic corundum have long been invented. How to determine which variety you are dealing with?

The photo below shows an artificial sapphire under a microscope. Its synthetic nature is revealed by bubbles – light and dark dots. An elongated bubble indicates a sapphire grown by the Verneuil method.

Outright fakes include products made of glass, plastic, and cheap minerals. It is not difficult to see the imitation.

  1. Due to its amazing hardness and density, real stone cannot be scratched by sharp objects. The fake one will have a visible stripe. But who will allow you to scratch jewelry in a jewelry store?
  2. A sure way to confirm the authenticity of a sapphire is by zoning – the uneven distribution of color in a natural stone. See the video below for more details.
  3. The gem will remain cool in your hands for a long time. The fake will heat up quickly.
  4. In bright light and under a magnifying glass, a heterogeneous structure is visible in the original; inclusions, tiny cracks, and chips are possible. The imitation is externally perfect.
  5. Under an ultraviolet lamp, the fake stone becomes greenish, while the reflections of the natural stone become white.
  6. If a cheaper gem, the so-called doublet or triplet, is passed off as a sapphire, then a thin layer of natural stone is glued onto the imitation, and the place of gluing is visible under a magnifying glass. A fake or similar semi-precious stone will be easily scratched by a precious sapphire.
  7. The cost of natural sapphire is high. Suspiciously low – an indicator of a cheap imitation.

Depending on the quality, there can be either a semi-precious or a precious sapphire stone. Cloudy corundum, speckled with cracks, is classified as semi-precious, ornamental, or even

Sapphires of artificial origin (grown) are not considered fake. However, this also does not apply to precious stones. Conscientious sellers do not hide the origin of the stone; they indicate this fact in the certificate, since synthetics are cheaper. It is difficult to find the differences on your own with the naked eye. Under a microscope, the boundaries between the overgrown layers are visible, similar to annual rings on a tree cut. Unless the ideal appearance and too bright shade will arouse suspicion.

Some people confuse sapphire with sapphirine. This is also a light blue colored gemstone. In time immemorial, he was called the “son of sapphire,” although they are not at all similar – neither in appearance nor in structure. Sapphirine is opaque and is classified as an oxide rather than an oxide. Cordierite, which is similar to it, is also not sapphire.

Main indicators of sapphire quality

The main quality indicators that characterize sapphires are: weight, color, purity, cut quality (it is determined in the same way as other colored stones).

Purity of sapphire

Blue sapphires usually have inclusions, but they usually have better clarity than rubies. Blue sapphires of extremely high purity are rare and very valuable. Sapphires contain several types of inclusions. Among them are long, thin mineral inclusions called needles. Fine needles are called silk when they occur as the mineral rutile in intersecting groups. Other characteristics of sapphire clarity include mineral crystals, partially healed fingerprint-like cracks, color zoning, and color bands.

Long, thin, intersecting inclusions of the mineral rutile are called silk. This arrangement can cause a star effect in the corundum.

Typically, inclusions make the stone less valuable. The price can drop significantly if inclusions threaten the durability of the stone. Even so, inclusions can add value to some sapphires. Many of the most valuable Kashmir sapphires contain tiny inclusions that give them a velvety appearance. They diffuse light, producing the desired visual effect, and do not negatively affect the clarity of the gemstone.

Sapphire cut

Oval shapes with triangular and serpentine edges on the crown of the stone (its upper part) and parallel rectangular edges on the stone pavilion (its lower part) are very characteristic of corundums of all colors.

The shape of the rough sapphire crystal affects the shape and size of the cut stone. The most common shape of a rough sapphire crystal is a barrel-shaped or spindle-shaped hexagonal pyramid.

To achieve the best overall color, maintain the best proportions, and maintain the highest possible weight, cutters focus on factors such as color zoning, pleochroism, and the lightness or darkness of the crystal—this allows them to best determine how to orient the stone during cutting.

Color zoning – the presence of areas of different colors in a gemstone – is a common characteristic of sapphire. Blue sapphire often has angular zones of blue and light blue. To accommodate the color zoning of some sapphires, cutters orient the concentrated color to the location that provides the best visible color of the cut stone.

In Sri Lankan sapphires, the color is often concentrated close to the surface of the crystal. If the cutter can orient the culet to a concentrated area of ​​color, then in the face-up position the stone will be completely blue. Pleochroism refers to different body colors in different viewing directions of crystals. Blue sapphires often have greenish-blue and violet-blue pleochroism. It is advisable to orient the cut so that, when inserted into the jewelry, the stone has a violet-blue color. Corundum is available not only in all colors, but also in all cut styles.

      • https://kamenis.com/sapfir/kakogo-cveta-byvajut-sapfiry-vidy/
      • https://provsekamni.ru/kamni/sapfir
      • https://dibora.site/ukrasheniya/kakie-czveta-byvayut-sapfiry-oni-vsegda-sinie/
      • https://UvelirnoeDelo.ru/sapfir/
      • https://journal.pierrejewellery.ru/priyatnyj-vybor/kak-vybrat-sapfir

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