The sapphire is one of the most popular gemstones in jewelry. It belongs to the corundum family, just like the ruby. Due to its exceptional hardness and beauty, sapphire has been used for centuries for jewelry and ornamentation. When the term "sapphire" is used alone, it refers to a blue sapphire. But there are many colors in sapphires, and when it is a color other than blue, it must be mentioned after the word sapphire, such as yellow sapphire, green sapphire, etc. Only red does not exist, because in this case we are talking about ruby.
Origins and Training
Sapphire forms under conditions of high pressure and high temperature, generally in metamorphic rocks (existing rock which, under the action of heat and pressure, undergoes a change in its structure and will give other rocks/stones. This happens in the depths of the Earth) or igneous (volcanic) rocks. It is composed of crystallized aluminum oxide (Al2O3) which is the basis of corundum, the mineral family to which sapphire belongs. Pure corundum is colorless. It is the presence of titanium and iron in trace amounts, in the crystal lattice, which is responsible for the blue color of sapphire. For other colors, we generally find in addition to these elements, magnesium for yellow, vanadium for violet…
The main sapphire deposits are found in Asia (Sri Lanka, which produces all colors of sapphire, Myanmar, Thailand), Africa (Madagascar, Tanzania), and Australia. Each region produces sapphires with distinct characteristics in terms of color and clarity, influenced by the local geology. Gemstone sapphires are also found in France, in the Massif Central. Production is very low and does not allow for mass supply of the jewelry market. But given the French craze for these stones, we are finding more and more. Especially since the deposits are not actually that small. They are also nothing like what we find in the countries mentioned above.
Physical and Optical Properties
Sapphire crystallizes in the trigonal/rhombohedral system.
The rough generally has an elongated structure with hexagonal faces and may have pyramidal terminations at one or both ends.
It has a hardness of 9 on the Mohs scale, which goes up to 10, which means it has a very high scratch resistance. Only diamond is harder. It can therefore only be scratched by diamond or another sapphire. This property comes from the compact crystalline structure of corundum, where each aluminum ion is surrounded by six oxygen ions in an octahedral configuration.
Sapphire has a specific gravity of 4, which is quite high. For the same weight, it will be smaller than most stones found in jewelry stores.
Optically, sapphire has a refractive index ranging from 1.760 to 1.770 and a birefringence of 0.008 to 0.010. These properties influence how light travels through the stone, contributing to its brilliance and shine.
Some sapphires exhibit optical phenomena such as asterism (starburst) or cat's eye, caused by microscopic inclusions of rutile needles. Sapphires must be cut into cabochons to bring out these phenomena.
Use in Jewelry
In jewelry, sapphires are often cut into oval or cushion shapes to maximize their brilliance and color. Cutting techniques take into account the orientation of the crystals to optimize light refraction and reflection. Star sapphires, which exhibit an optical phenomenon called asterism, are particularly prized for their rarity and unique beauty.
Meaning and Symbolism
Sapphire has long been associated with royalty and romance. It symbolizes wisdom, virtue, and good fortune. Throughout history, sapphires have often been used in crowns and royal ornaments. Today, it is also popular in engagement rings, especially since Princess Diana received a sapphire ring upon her engagement to Prince Charles.
Maintenance and Preservation
To preserve the brilliance of sapphires, it is recommended to clean them regularly with warm water and mild soap. They should be stored separately from other jewelry to avoid scratching them or each other. Although sapphire is very durable, it can be damaged by strong impacts.
Treatments and Syntheses
Like anything of value, various techniques have been used to increase profits and turn low-quality sapphires into jewelry-grade gems or simply create synthetic sapphires that are cheaper to produce.
Treatments
The only treatment that is accepted and does not devalue the price of a sapphire is so-called traditional heating, up to 800-900°C. This practice has been carried out for centuries and is considered "an extension of what happens underground." It does not alter the stone and changes little or no inclusions present in the sapphire. Sometimes very difficult to diagnose with gemological tools alone when the stone is perfectly clean. Laboratories can detect it. An unheated sapphire will still be more expensive than a heated sapphire. Many heated sapphires are sold as unheated since it is not easy or even impossible to diagnose on very clean stones for a field gemologist.
Apart from this treatment, here are the pitfalls that one may encounter when wanting to buy a sapphire:
- Imitation stone : A blue-colored stone or imitation stone like glass that resembles a sapphire. A gemologist will be able to spot it very easily. Some beautiful kyanites have already been sold as sapphires because they can have a very similar color.
- Very high temperature heat treatment : The structure of the sapphire is altered, the inclusions are modified. This allows stones that are not beautiful, translucent, to be transformed into beautiful sapphires of higher value. They are not worthless! But their value is still significantly lower than a natural sapphire or one that has undergone traditional heating.
- Very high temperature heat treatment with addition of additive : In addition to heating, the sapphire is placed in the presence of titanium or beryllium.
For titanium, this is done on an already cut stone. The titanium will diffuse onto the surface of the sapphire and make it very blue. The coloring is only on the surface. If the stone is recut, the blue will be removed. The color is generally quite dark. You can dip the sapphire in diiodomethane to see if a sapphire has been diffused; it loses its color. But as always, counterfeiters are improving, and we now find titanium-diffused sapphires that are quite difficult to diagnose without the help of a laboratory.
For beryllium, it can be done on raw sapphires. Beryllium, which is smaller, will diffuse throughout the stone. This will completely change the color of the sapphire. You can recut the stone, it won't change its color. At first, it produced pink sapphires, but now we find many colors. Orange-red, yellow... the color is pretty, but a gemologist can quite easily recognize that the color is not natural. Then there are always stones that raise doubts because nature can also produce stones in these colors. Laboratories can detect this treatment, just like the diffusion of titanium.
- Heat treatment with fillers . At first, heated and therefore liquid glass was used so that it penetrated the cracks in the stone to fill them and mask them. This technique can turn a really not-so-great sapphire (or ruby) into a very beautiful sapphire. Under a magnifying glass, under certain conditions, you can see what is called a flash effect at the filled crack because of the difference in refractive index between the glass and the corundum. Now, lead and/or various products are added to limit the flash effect, to reduce the heating temperature... everyone has their own little secret recipe. There are even some who add aluminum oxide, which is the basic component of corundum, so that it recrystallizes in the cracks. In this case, it is very difficult, if not impossible, to diagnose because it is filled with the same material.
Filling treatments significantly devalue the price of stones and are usually hidden. Depending on how this treatment is performed, it may or may not be detectable by a gemologist.
The syntheses
If we've managed to avoid the previous pitfalls, we now need to be careful with synthetics! And that's another story! Because a synthetic has exactly the same physical and optical characteristics as natural sapphire. Because it's exactly the same thing! Except that one is man-made and the other is earth-made. They don't have the same history. The natural one is several million years old.
There are several different synthesis processes that produce sapphires of varying purity. The main processes are Verneuil, anhydrous, and hydrothermal.
Those generating the purest are the most complicated and most expensive to make (anhydrous and hydrothermal).
Each type of synthesis has its own characteristics, characteristic inclusions that can help identify them. These inclusions are generally very difficult to see and you really need experience to detect them. Especially since the people manufacturing these syntheses are constantly seeking to improve to achieve perfection; the goal is not necessarily to deceive people but also for the needs of the industry.
In jewelry, the most common process, because it's the simplest and least expensive, is the Verneuil process. It's also the easiest to detect, but counterfeiters are improving every day.
We find many of these productions near the mines to deceive buyers because logically the closer we are to the mines the more we think we are buying natural sapphires...
And it's getting harder and harder to detect them without going through a lab. That's why it's sometimes better to have a sapphire that's not completely clean with a few small inclusions invisible to the eye to be sure it's natural. After all, synthetic sapphire manufacturers don't do it to scam people! There's a high use of sapphires in the industry that demands very pure sapphires.
Scientific and Industrial Applications
In addition to its use in jewelry, sapphire has important industrial applications. Thanks to its hardness and chemical resistance, it is used in the manufacture of electronic components and high-precision optical instruments. In these cases, of course, we are talking about synthetic sapphires, produced using techniques such as the Verneuil process, but also anhydrous and hydrothermal sapphires when the need for purity is very high. We say sapphire, but for industry, it is actually corundum, which is sapphire without the color.
In conclusion, sapphire is a gemstone that combines beauty, durability, and remarkable scientific properties. Its wide range of colors and optical qualities make it a prime choice for fine jewelry, while its industrial applications demonstrate its usefulness beyond ornamentation. However, it's important to purchase from a knowledgeable and honest person to avoid the fakes we just saw.
On the Passot-Gems website, you won't find a summary. Treatments, if any, are clearly specified. Currently, the only treatment you'll find here is traditional heating.
