HomeMajor Colored StonesAlexandriteAlexandrite
Introduction and History
Alexandrite is the colour-change variety of the mineral  species chrysoberyl, and is the one of the birthstones for June.  Alexandrite is said to enable its wearer to foresee danger.
 

This rare gemstone is named after the Russian tsar Alexander II (1818-1881), the very first crystals having been discovered in April 1834 in the emerald mines near the Tokovaya River in the Urals. The discovery was made on the day the future tsar came of age. Although alexandrite is a relatively young gemstone, it certainly has a noble history. Since it shows both red and green, the principal colours of old Imperial Russia, it inevitably became the national stone of tsarist Russia.



Beautiful alexandrite in top quality, however, is very rare indeed and hardly ever used in modern jewellery. In antique Russian jewellery you may come across it with a little luck, since Russian master jewellers loved this stone. Tiffany’s master gemmologist George Frederick Kunz (1856-1932) was also fascinated by alexandrite, and the jeweller’s firm produced some beautiful series of rings and platinum ensembles at the end of the 19th and beginning of the 20th century. Smaller alexandrites were occasionally also used in Victorian jewellery from England.

The most sought after alexandrites are a lovely green in daylight or fluorescent light, but change to red or slightly purplish red in the incandescent light from a lamp or candle flame.

Abundant alexandrite deposits were first discovered in 1830, in Russia's Ural Mountains.  Those first alexandrites were of very fine quality, and displayed vivid hues and dramatic colour changes.  The gem was named after the young Czar Alexander II, and it caught the country’s attention because its red and green colors mirrored the Imperial Russian flag.

The spectacular Ural Mountain deposits didn’t last forever, and now most alexandrite comes from Sri Lanka, Brazil, India, Tanzania, and Madagascar. The newer deposits contain some fine-quality stones, but many possess less precise colour change and muddier hues than the 19th century Russian alexandrites.  Some of the famed Ural Mountain alexandrites can still be found in estate jewellery.  They remain the quality standard for this phenomenal gemstone.

Judging Quality and Buying

Most expensive of the chrysoberyls are the alexandrites, which are among the most expensive of all gemstones. Even melee can fetch hundreds of dollars per carat, and fine stones of over one carat are priced in the thousands. The ideal in alexandrite is a stone which displays a daylight colour like the finest Colombian emerald, shifting to the colour of a fine Burma ruby in incandescent light. 
Chemistry and Crystallography
Chemical Composition  
Crystallographic System  
Cleavage  
Fracture  
Fracture Lustre  
Habit  



Physical Characteristics

Hardness  
Toughness  
Specific Gravity  
Streak  



Optical Characteristics

Colour and Cause  
Degree of Transparency  
Polish Lustre  
Refractive Index  
Birefringence  
Optic Character  
Pleochroism  
Dispersion  
Phenomena  
X-Ray Fluorescence  
Transparency to X-Rays  
Ultraviolet Fluorescence  
Chelsea Filter Reaction  
Absorption Spectra  



Description

Appearance  
Variety and Trade Names  
Misnomers  
Typical Size Range Alexandrites typically come in sizes from melee to 5 carats. Larger stones are rare.
Typical Cutting Styles  

Inclusions 
Alexandrites are typically transparent, and may contain fingerprint and silk inclusions.
Occasionally, distinguishing natural from synthetics has been difficult, notably for flux-grown synthetics, but especially when a specimen lacks diagnostic mineral inclusions. These difficulties are caused by the similarity of growth structures and healing "feathers" in natural alexandrites from different localities to residual flux featheres in flux grown synthetic alexandrites. Haematite platelets in natural alexandrites sometimes resemble platinum inclusions in their flux-grown synthetic counterparts.

Treatments 
None known

Synthetics
Czochralski and flux grown alexandrites exist

Origin 

Locality 
Sri Lanka and Brazil are the two major producers.   Alexandrite is also found in Madagascar, Tanzania, India, Sri Lanka, and Russia.
During the past 10 years, new deposits of natural alexandrites have been found in Minas Gerias, Brazil(Bank et al., 1987; Proctor,1988; Cassedanne and Roditi,1993; Karfunkel and Wegner, 1993); in Orissa and Madhya Pradesh, India(Patnaik and Nayak, 1993; Newlay and Pashine, 1993) and most recently near Songea in southern Tanzania. Gem alexandrites are still being recovered from the historic emerald deposits of the Ural Mountains.

Care

Cleaning Methods ultrasonic: Usually safe
steamer: Usually safe
warm soapy water: Alexandrite can be cleaned in warm, soapy water
Stability reaction to heat:
stability to light:
reaction to chemicals:

Market 
Availability  
Public Recognition  
Wearability  
Recommended Disclosures  
Value  

Key Separations, Suggestions for Testing and Evaluation
  • Synthetic alexandrite was developed in 1973.   It can be grown using the flux or Czochralski methods. Synthetic alexandrite will have a similar color change to natural alexandrite, bluish green in daylight and brownish red to purple-red in incandescent light. Synthetic alexandrites often have flux inclusions, triangular metallic platelets, curved striae, or gas bubbles, depending on the growth technique that was used to grow the synthetic. Synthetic alexandrites typically have a slightly lower RI, and stronger fluorescence than natural alexandrites.
  • Synthetic color-change corundum (of which ruby and sapphire are varieties) was developed approximately in 1909. The color change in alexandrite-like synthetic sapphire will be bluish purple or greenish blue changing to reddish purple, depending on the growth process used to create the synthetics.
  • Synthetic color-change spinel.
  • Color-change garnet
  • Color-change sapphire

Possibilities for Confusion


Bibliography and Suggested Further Reading
http://www.gia.edu/library/28235/featured_gemstone__alexandrite.cfm 

Introduction
Alexandrite is the variety of chrysoberyl that displays a change-of-color from green to red. A distinct color change is the primary qualification for a chrysoberyl to be considered alexandrite. Although alexandrite is strongly trichroic, its color change has nothing to do with pleochroism. Instead, like all other color-change gems, it results in a near-equal transmission of the blue-green and red portions of the spectrum, coupled with strong absorption in the yellow. Thus its color is dependant on the spectral strength of the light source. Incandescent light is strongly tilted to the red end, thus causing alexandrite to appear reddish. Daylight, is more equally balanced. Since our eyes are most sensitive to green light, the balance is tipped to the green side. The strength of the color change is related to the difference in the areas of transmission, relative to the absorption in the yellow. The greater the difference, the stronger the color change.

Alexandrite photo image
This 1.89-ct. alexandrite, here shown in daylight (left) and incandescent light (right) comes from the famous Russian mines. Gem courtesy of Pala International.
(Photo: This email address is being protected from spambots. You need JavaScript enabled to view it.; Gem: Pala International)

Color
For alexandrite, the quality of the color change is paramount. While the holy grail is a gem whose color changes like a traffic light from green to red, such a stone has yet to be found. In fine examples, the change is typically one from a slightly bluish green to a purplish red. The quality of color change is often referred to by dealers in a percentage basis, with 100% change being the ideal. Stones that display a change of 30% or less are of marginal interest and are arguably not even alexandrite. Significant brown or gray components in either of the twin colors will lower value dramatically.

Clarity
In terms of clarity, alexandrite is comparable to ruby, with clean faceted stones in sizes above one carat being rare and extremely rare in sizes above 2–3 carats. Negative crystals and parallel rutile silk are common inclusions.

Cut
In the market, alexandrites are found in a variety of shapes and cutting styles. Ovals are cushions are the most common, but rounds are also seen, as are other shapes, such as the emerald cut.

Alexandrite photo image
This 1.02-ct. alexandrite, here shown in daylight (left) and incandescent light (right) shows a nice color change. Gem courtesy of Pala International.
(Photo: This email address is being protected from spambots. You need JavaScript enabled to view it.; Gem: Pala International)

Prices
Alexandrite is one of the world‘s most expensive gems, with prices similar to those fetched by fine ruby or emerald. But like all gem materials, low-quality (i.e., non-gem quality) pieces may be available for a few dollars per carat. Such stones are generally not clean enough to facet.

Stone Sizes
Facet-quality alexandrite rough is extremely rare. Thus even melee (less than 0.5 ct.) can sell for thousands of dollars per carat. Any fine faceted alexandrite above two carats should be considered quite large. Stones of quality above five carats are extremely rare. While Sri Lanka has produced some alexandrites above 10 carats, these generally do not display a good color change, moving from green to brown.

Name
The name “alexandrite” was coined by mineralogist Nordenskjöld, in honor of the former Russian czar, Alexander II, who came of age about the time the gem was discovered (supposedly on 23 April, 1830). An added factor was that the old Russian imperial colors of red and green are also the colors of alexandrite.

Sources
The original locality for alexandrite is Russia. Fine stones have also been found in Sri Lanka, Zimbabwe, Burma, Tanzania, Madagascar, India and Brazil. In 1987, an important new deposit at Hematita, Brazil was discovered. This mine produced for just a brief period, but a number of fine stones were found. In the mid-1990’s, Tanzania’s Tunduru region has also produced some outstanding specimens.

Imitations
While true synthetic alexandrites do exist, the vast majority of such stones are actually synthetic color-change sapphires colored by vanadium. Since synthetic color-change sapphires have been made from about 1909 onwards, it is entirely possible to have a piece that is nearly an antique. Indeed, many a traveler has returned from a third-world trip with what they think is natural alexandrite, only to later discover (or have their heirs discover) that what they have is a cheap synthetic sapphire worth but a few dollars per carat.

Alexandrite photo image
This 5.25-ct. alexandrite, here shown in daylight (left) and incandescent light (right) is an example of the finest of this gem variety. It comes from Tunduru, Tanzania, and was recently sold by Pala International.
(Photo: This email address is being protected from spambots. You need JavaScript enabled to view it.; Gem: Pala International)

Properties of Alexandrite

  Alexandrite (a variety of chrysoberyl)
Composition BeAl2O4
Hardness (Mohs) 8.5
Specific Gravity 3.74
Refractive Index 1.746–1.755 (0.009) Biaxial positive
Crystal System Orthorhombic
Colors Daylight: Green to blue-green
Incandescent Light: Purple to purplish red
Alexandrite is colored by the same Cr+3 ion that gives ruby and emerald their rich hues. Rarely, vanadium may also play a part
Pleochroism Strongly trichroic: greenish, reddish and yellowish
Phenomena Change of color, cat’s eye
Handling No special care needed
Enhancements Generally none; occasionally oiling, dying
Synthetic available? Yes

Who are we?

The Geohavens name is an assurance of timeless beauty, distinct quality and uncompromising value. The Company spares no effort in sourcing from the farthest markets and the deepest mines in order to unearth the most attractive gems.

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