Alexandrite Overview

Alexandrite stone is a type of stone that changes color as a cause of sunlight, during daylight it appears to be a bluish green mix but with shade and different rays of light exposure on it, color differentiates. The alexandrite stone is worn by the people born in November and also recommended for the zodiac signs Aquarius and Scorpio. Original alexandrite is stone was the first time discovered in Russia’s Urals mountains in the 1830s. Now it’s found in different countries of the world like Srilanka, South Africa, and Brazil.

Occurence and Mining

After the discovery of a gem mineral with unusual color-change behavior in the Russian Ural Mountains during the early 1830s, Swedish mineralogist Nils Adolf Erik Nordenskiöld named this new gem alexandrite in 1834 in honor of the future Czar Alexander II (Kozlov, 2005). This immediately created a royal and romantic aura around this variety of chrysoberyl. The most coveted alexandrites exhibit a lush green to greenish blue color in daylight and a warm, bright red shade in candlelight (Levine, 2008); some fine Brazilian and Indian alexandrite examples are shown in figures 1–3 and 6. This phenomenal color change is caused by the presence of trace Cr3+ substituting for Al3+ in the chrysoberyl crystal structure. Alexandrite is routinely described as “emerald by day, ruby by night.” It is a stone of duality—green or red, cool or warm, day or night (Levine, 2008). Because of its rare and attractive color-change phenomenon, alexandrite has been highly sought after and is one of the most valuable gemstones in the trade. Alexandrite, particularly fine-quality material, is also very scarce; it has generally been a byproduct of mining other major colored stones. Overall production statistics are hard to evaluate. It has been mined in Russia (Kozlov, 2005; Schmetzer, 2010), Tanzania (Gübelin, 1976; Schmetzer and Malsy, 2011b) and Zimbabwe (Brown and Kelly, 1984; Schmetzer et al., 2011) as a byproduct of emerald mining, and in Brazil (Proctor, 1988; Cassedanne and Roditi, 1993; Voynick, 1988) and India (Newlay and Pashine, 1993; Patnaik and Nayak, 1993; Panjikar and Ram¬¬¬¬chan¬¬dran,1997; Voynick, 1988; Valentini, 1998) along with cat’s-eye and nonphenomenal chryso¬beryl, as well as other pegmatitic minerals. In Sri Lanka (Zwaan, 1982; Zoysa, 1987, 2014), it is mined as a byproduct of corundum, cat’s-eye and nonphenomenal chryso¬beryl, and other minerals. The supply of alexandrite in the U.S. market has been low since the 1990s, as the supplies from the initial rush in Brazil presumably started drying up (Costanza, 1998). However, demand for the gemstone has stayed high in the U.S., especially for large stones with high clarity and intense and distinctive color change (again, see figures 1–3 and 6).

Quality Factors

Color and color change are the most important quality factors for an alexandrite and are the primary drivers of value. General rule is that as color saturation of an alexandrite increases, the value increases. The second and equally important factor is the color change. The more dramatic the change is between incandescent and daylight, the more valuable it becomes.
Colored gems do not have a standardized grading system and it is extremely rare to find an Alexandrite with no eye visible imperfections. This is in stark contrast to Diamonds which have a standardized grading system and require magnification to inspect clarity. In the wholesale trade we evaluate alexandrite clarity using the following methodology
Lapidaries cut alexandrites according to the shade of the rough material to get the desired color (the primary price driver). Darker material is cut shallower to allow more light to go through the gem, while lighter material is cut deeper to allow the alexandrite to hold in more light and increase saturation. The lapidary also must factor in the color change when cutting the gemstone. Alexandrites also possess unique cleavage properties that makes it difficult to cut. Cutting alexandrite is an art and requires years of experience. Transparent gems are the most valuable and allow one to see the true richness of color. The catch-22 with transparent gems is that it is much easier to view imperfections. Finding an alexandrite transparent and eye clean is truly rare. Over-saturation of color leads a gem to be semi-transparent as less light is allowed to escape. Opaque gems tend to be eye clean, but may appear as black.
The weight of a gemstone is measured in a unit called carats (cts.). There are 5 carats in 1 gram. As discussed above, an alexandrite can be cut deep or shallow to maximize the color of the sapphire. A deep cut 1 carat alexandrite will appear visually smaller than a 1 carat shallow alexandrite. For this reason, it is best to judge an alexandrite based on millimeter measurements (length and width) and not carat weight. Which you can print to see the actual sizes of various shapes.

Identification

Color

a bluish-green in daylight and fluorescent light

Crystal habit

As crystals, Orthorhombic.

Refractive Index

1.739 to 1.770+

Optical Character

Biaxial/+,-

Birefringence

0.007 to 0.013

Pleochroism

Red stones – strong trichroism: dark red – orange – dark green

Refractive Index

1.739 to 1.770+

Optical Character

Biaxial/+,-

Birefringence

0.007 to 0.013

Pleochroism

Red stones – strong trichroism: dark red – orange – dark green

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