Alexandrite Gemstones - Color-changing valuable gems
Introduction
Alexandrite is part of the Chrysoberyl group of stones, and are said to have an aluminum and beryllium composition. The name Chrysoberyl, is taken from the Greek word which means "A golden-white spar" Chrysoberyl and Beryl may have similar names but they are completely different gemstones. Chrysoberyl has a very hard value and is the third-hardest gemstone in the world. It has a value of 8.5 on the Mohs scale. Corundum has a value of 9 and diamond a value of 10. The crystals of Chrysoberyl have a characteristic cyclic twin structure that is known as Trilling. These crystals, are actually a triplet of twins, which have a hexagonal appearance; each has a 120 degree orientation to the next. A V-shaped twin results when any of the three twins have the twin orientations. Chrysoberyl has a yellowish green appearance, and has a clarity that varies from transparent to translucent. Now you may wonder why the introduction to Alexandrite has to begin with an introduction to Chrysoberyl. There are three main varieties of Chrysoberyl; the traditional yellow-green Chrysoberyl, the one that resembles a cat´s eye, called the Cymophane and finally the Alexandrite.
In partially polarized light, and depending on the angle of viewing, Alexandrite will exhibit emerald green, orange-yellow, and red colors; the stone has strong pleochroic characteristics. Another characteristic of Alexandrite is the fact that is can also change colors when exposed to artificial lighting. And not only in natural light. The color change is brought about by the fact that it absorbs the yellow spectrum of light, which is quite narrow, and allows the larger bands of red and blue-green light to be transmitted. Depending on the spectral balance of the lighting, you will either see the red colors, or the blue-green colors. When you look at fine alexandrite along the main axis in natural light, it will give out a blue, or greenish blue color, which tends to a string blue in high temperatures, and this will change to purple-red hues when the lighting is artificial, which has a lot of yellow wavelength. Fine Alexandrite is very rare to find, and those that are commonly found show colors of yellowish-green color during the day, and this will change to a brownish red color when viewed in incandescent light.
The formation of Alexandrite
Chrysoberyl, which is the main species of which the variety Alexandrite belongs, is formed due to what is known as the pegmatite process. In this process, the molten crust of the earth, gives off a low-density mass of molten magma, which rises slowly through the strata towards the surface. As the magma begins to cool on rising to the surface, the water which was present is concentrated more, because it cannot be incorporated into the crystallization process. Similarly, remnants of minerals which cannot also be added to the crystals of the other minerals are left in the water, and the resultant magma has a lot of water and non-crystalized minerals. The water, flows down the magma, and allows for these non-crystalized minerals to come together and form their own distinct crystals, which are dissimilar from the crystals of the rocks around them. The rock that is thus formed has an igneous appearance, but has been formed at low temperatures, from melted minerals, such as feldspar and quartz, that are rich in water molecules, but also have a lot of beryllium, niobium and lithium, and these are what form the rocks that are called pegmatite. The concentrated water levels in the magma allow the crystals to quickly grow, and this is how the gems specimens form.
Alexandrite can also be found in the rocks that form around such pegmatite; this only happens when water and fluids that have a lot of Beryllium and aluminum flow into the rocks from the pegmatite allowing the crystals to form within the rock structure. This is the reason why this gemstone can also be found in schist of mica and also deposits of the metamorphic dolomite marble rock. Since the crystals are very hard, they are released into rivers and streams when the surrounding rock is eroded by the action of the water. Alluvial deposits are also found to have a lot of such crystals. Such alluvial deposits have also been found to have diamonds, Spinel, Garnets, and Tourmaline among many other hard crystals. When found in alluvial deposits, Alexandrite will have a rounded shape, rather than the sharp edges that are found when mined directly from the rock. In Brazil and Sri Lanka, the main sources of Alexandrite are alluvial, as they are released by the process of weathering or the surrounding rocks.
Why is alexandrite so rare?
In order to understand why alexandrite is rare, you have to understand the physical properties of its components. Pegmatite fluids will normally lead to the formation of Beryl, which has a higher ratio of beryllium than aluminum, and Chrysoberyl, where the opposite is true. When they are in the presence of quartz, the two minerals are stable and no more reactions go on. However, in order to form alexandrite, there has to be some chromium present. Here lies the reason why alexandrite is rare, Chromium and beryllium hardly ever occur within the same rock structures. The rocks that contain chromium are called mafic or ultramafic rocks, and finding beryllium in such rocks is rare. On the other hand, beryllium is commonly found in felsic pegmatite and in such rocks, the presence of chromium is rare. This means that alexandrite can only be found in in areas where the pegmatite fluids, which are rich in beryllium, react with country rocks, which are rich in chromium. This is a very erratic occurrence and this is why alexandrite is very rare.
Depending on the color of the ambient light, alexandrite will display a wide range of colors as a result. This phenomenon has been given the term, "the Alexandrite effect", and it refers to the changing of color from a greenish tint, to a reddish one, as the source of the light changes. You need to understand that Alexandrite forms due to the replacement of aluminum, by chromium, in the crystals structure. This chromium absorbs a very narrow band of yellow light, in the visible spectrum, and allows the other wavelengths to be emitted. The human eye is more sensitive to the red and green spectrum, and this is why the stone looks green when it is viewed in the daylight, and red when viewed in tungsten light. Unlike pleochroism, which refers to the changing of color due to the angle of viewing, the alexandrite effect is the same even as the stone is rotated, but the colors will change when the nature of the light changes, due to the main wavelengths of the light source; natural light emits the full spectrum, while the incandescent source emits more of the blue and green wavelengths. The Alexandrite mined in the Russian Ural Mountains seems to be green during the day, and red when bowed in incandescent light. Other varieties of this gemstone are yellow or pink during the day and raspberry, or columbine when viewed in artificial light. The changes in color are usually very subtle, but in rare stones, the changes in color are very dramatic; these stones are highly sought-after and fetch a handsome price.
A brief history of alexandrite
There is a controversial but popular story about the discovery of alexandrite. It is said that a mineralogist from Finland, who lived between the years of 1792 and 1866, known as Nils Gustaf Nordenskiüld, discovered the gemstone. It is said that he named the stone alexandrite, after the future Tsar of Russia, Alexander II, who had just become of age when he discovered the stone. It is said that a new mineral was discovered in Perovskii, by his field team, and when it was sent to him, he realize that this was a new gemstone, after careful examination. At first, he thought that the stone was an emerald, but later changed when he realized there were significant differences in the structure of the stone.
The reason why the stone was first through to be an emerald was the fact that it was found near the emerald mines at the Tokovaya River in the Urals. This was in April 1834, when the Russian Emperor, Alexander II, came of age; Alexander lived between the years of 1818 and 1881. When compared to other gemstones, Alexandrite is considered to be a rather young gemstone, but it has a great history among royalty. It soon became the national gemstone of Tsarist Russia, since it showed both the green and red colors which were part of the national colors of the ruling party then.
As far as size is concerned, it was said that stones of sizes larger than 5 carats could only be found in the Ural Mountains, but lately, there have been larger stones from areas such as Brazil. In Madagascar, Sri Lanka Tanzania and India, you can also get alexandrite in sizes of over 3 carats. Getting large stones is usually very rare, given that even the smaller stones are relatively rare when compared to other gemstones.
Lab grown alexandrite: is it synthetic or simulated?
It is possible to get alexandrite, grown in a laboratory which has similar characteristics to the naturally occurring specimen. In ne if the methods, called the flux-growing method, the alexandrite is produced in such a manner that one cannot easily tell the difference between the natural and lab-grown variety. This is because the method used gives the stones a characteristic inclusion pattern that is similar to that of naturally occurring alexandrite. The other method is the Czochralski, or Pulled Alexandrite method, in which the resultant mineral has a very clear transparency. It is easy to tell the different between pulled alexandrite and the natural variety. The stones are extremely clean and they tend to have curved striations which can be seen through the magnification glass. Pulled alexandrite exhibits the traditional color change from green to red, when viewed in natural and incandescent light, but this change does not resemble that of natural alexandrite.
There are gemstones, which are said to be lab-grown alexandrite, but are actually corundum stones which have been laced with certain trace elements such as vanadium. They can also be Spinels, which are able to change colors, and cannot be characterized as Chrysoberyl, the group to which alexandrite belongs.
This is the reason why such stones are said to be simulated alexandrite, since they only simulate the characteristics of alexandrite but cannot be classified as such. The stones which are grown using the Pulled Alexandrite and Flux Alexandrite methods can be termed as synthetic alexandrite since they resemble the original ones in structure and also physical appearance. Simulated alexandrite has been grown for over 100 years and has a characteristic purple-mauve color, and has some similarities to sapphires; there is never any green color in these stones.
It is very rare that you actually get a beautiful and natural alexandrite crystal; in modern jewelry, most alexandrite designs will be created from synthetic or simulated alexandrite. Master Russian jewelers loved making jewelry using natural alexandrite, so if you come across any antique Russian jewelry, then you will have a natural stone in the setting. The master gemologist as Tiffany´s, George Frederick Kunz, who lived in the period of 1856 and 1932, loved using alexandrite in his creations; there are fine platinum jewelry, that has alexandrite, which he created at the end of the 19th Century and the start of the 20th century. Victorian jewelry from England also contains smaller natural alexandrite gemstones.
Something about the magical changing of colors
One of the reasons why the alexandrite is so sensational is the ability to change colors, when the source if the light changes. In natural light, the stone looks green or bluish green, but when it is placed in incandescent light, it looks reddish or pinkish in color. This is one of the reason why this stone is very much in demand, especially when it can be found in fine qualities.
Due to its unique chemical composition and formation, alexandrite is very rare in nature. In broad terms, an alexandrite stone can be categorized as a Chrysoberyl, which is normally colorless, or transparently yellow when in pure forms. Chrysoberyl cat´s eye, and the color-changing alexandrite, are Chrysoberyl gemstones that have impurities in them. Alexandrite has a lot of iron and titanium, but the element that is responsible for the color changes is chromium. On rare occasion, the presence of vanadium will also play a role in the changing of colors in this gemstone. In the nomenclature of alexandrite, only Chrysoberyl gemstones which can actually change color when passed from natural to incandescent light, can be termed as being true alexandrite.
Most gemstones were formed millions of years ago, in metamorphic conditions, when the crust of the earth moved, but in the case of alexandrite, there had to be specific geological conditions for the crystals to form. Beryllium, which is a major constituent of all Chrysoberyl stones, and Chromium which is the agent that gives alexandrite its characteristic color, do not occur together, unless under specific conditions; their chemical characteristics make sure that they rarely are found in adjacent areas, where they can combine to form alexandrite. In areas where rocks containing the two elements are brought together, there had to be NO silica, which is the most abundant mineral on earth, since the presence of silica would lead to the formation of emeralds, rather than alexandrite. In the history of the earth, this is a geological scenario that occurred very rarely, and this is why this gemstone is so hard to come by.
Russia is not the only source of alexandrite gems anymore
Since the popular stones from the mines of the Ural Mountains, entered the market, the main source was always the Russian mountains. There was a time when people thought that the Russian deposits of the gemstones were depleted and the demand for this color-changing gemstone went down. Alexandrite from other mines did not display the coveted color change. In 1987, the situation changed drastically, and alexandrite were discovered in a place called Hematita, in an area of Brazil known as Minas Gerais. The stones that came from Brazil were found to have the desired color change and the somewhat low demand for the gemstones once again started to rise. One cannot say that the Brazilian alexandrite had as intense a color as the Russian variety but the change in color was quite apparent. In terms of economic terms, Hematita is one of the most important alexandrite deposits on the planet. Alexandrite from this place are occasionally known to show chatoyancy, which is a phenomenon that has not been observed in any of the Russian specimens.
Alexandrite can also be found in Sri Lanka, but the intensity of their color is very poor when compared to that of stones mined from the Urals. They have a dull green color during the day, and a brownish red appearance at night. In Southern Tanzania, in an area known as Tunduru, some outstanding alexandrite crystals have been mined ever since the mid-1990s.
There are other deposits of alexandrite in Burma Madagascar, India and Zimbabwe, and you can only find the gemstone in specialist jewelry shops, since the stone is very rare. The strengthening of trade ties between Russia and the rest of the world has allowed specialist shops from all over the world to stock original alexandrite from the Urals.
Fine characteristics for fine jewelry
Alexandrite is said to be one of the hardest minerals on the planet, and has a value of 8.5 on the Mohs scale; with such a value, it is a stone that is easy to wear and to take care of. The value of the stone increases as the distinction is the color increases, which means that the more apparent the color change then the more precious the stone will be. Fine alexandrite is said to be vividly green in color, with a tinge of blue, when viewed in daylight, and a deep red color, with a purple tinge when viewed under incandescent light; the fine stones will not have any hints of the undesirable grey or brown hints under any lighting condition. It is a given that a stone is rare and of great value, when it is proven, beyond all doubt, that the origin was the Ural Mountains of Russia. You should not be surprised to find fine alexandrite jewelry, that has lovely facets, costing a lot more than similar jewelry made from fine sapphires, rubies or emeralds; quite a fascinating fact, given that the stone is quite unknown to the common person.
Some more information about alexandrite gemstones
Alexandrite is considered to be a true understatement gemstone, given that it is not in high demand amongst the common jewelry buyers, who would rather go for emeralds and rubies; this is a gemstone that is a preserve of experts, connoisseurs and collectors. It is not possible to tell the high value of the stone, and the magical color change, when you first look at it. However, if you are a true gemstone lover, and have never seen this magical stone, then you will be absolutely fascinated when you first lay your eyes on it. Due to the magical changing of colors, people say that the stone brings about good luck to the wearer, and you may also feel this magic, when you first see how it changes colors during the day and night. People also believe that the stone will serve as a good omen, and sharpen the intuitive powers of the wearer, thereby allowing him or her to get through even the toughest of situations, through the use of intuition rather than logic. It is said to inspire creativity and tickle the imagination.
If you want to buy an alexandrite piece of jewelry, then you should know that the color of the stone is what sets the value. After the color, you can now consider the other factors such as carat weight and clarity of the stone. When in its purest form, alexandrite will show different colors depending on the source of light. This means that it will look like an emerald during the day, look reddish when viewed in incandescent light, seem purple when viewed under candlelight, and also look almost green in florescent light. The alexandrite is considered as the birthstone for the month of June and it is also given as the gemstone for the 55th Anniversary. Alexandrite should always be cleaned in warm and soapy water, and a brush used to remove dust that may be stuck in the setting. It is a tough gemstone and can be worn at any time or day.
