Alexandrite’s quality factors - ICKINGER |

Quality Factors:


In this post we will be discussing the Alexandrite’s quality factors such as colour, clarity, cut and carat weight.


Colour:


Fine alexandrite is green to bluish-green in daylight and red to purplish-red in incandescent light. Its colour saturation is moderately strong to strong. Stones that are too light do not reach the quality of colour intensity seen in fine-quality gems.

Stones that are too dark lack brightness and appear almost black. Sri Lankan alexandrites are generally larger than their Russian counterparts, but their colours tend to be less desirable. The greens tend to be yellowish compared to the blue-green of the Russian stones, and the reds of Sri Lankan alexandrite are typically brownish-red rather than purplish red.


Clarity:


Alexandrite tends to contain a few inclusions. There’s a dramatic rise in value for clean material with good colour change and strong colours. When certain types of long, thin inclusions are oriented parallel to each other, they can create an additional phenomenon called chatoyancy, or the cat’s-eye effect, increasing the alexandrite’s value.


Cut:


Alexandrites are most commonly fashioned into what are called mixed cuts, which have brilliant-cut crowns and step-cut pavilions. Brilliant cuts have kite-shaped and triangular facets, while step cuts have concentric rows of parallel facets.

Alexandrite’s pleochroism makes it a challenge for cutters. When fashioning alexandrite, cutters orient the gem to show the strongest colour change through the crown. It’s crucial to position the rough so the fashioned stone shows both purplish-red and green pleochroic colours face-up.


Carat Weight:


Most fashioned alexandrites are small, weighing less than one carat. Larger sizes and better qualities rise in price dramatically.





Is there a difference between “Russian” and “Brazilian” Alexandrite gemstones?


From a historical standpoint it is evident that Russian alexandrites are by far the most sought after gemstones since its discovery, however, Brazilian alexandrites may be better according to the Alexandrite tsar stone collectors guide. With better clarity and a strong colour change from rich blue-green to strong purple-red, the beautiful colour change of the Brazilian alexandrites is highly prized and the stones are always in strong demand.

With so few Russian alexandrites available anywhere, their quality is nearly impossible to compare with alexandrites from later discoveries. Some fine alexandrites have been found at every important alexandrite deposit and the qualities of the best stones, as evidenced by the high prices they have fetched must surely rival even the very best Russian stones.


What causes the cat’s-eye effect in chrysoberyl?


The cat’s-eye effect is caused by the reflection of light off of minute, parallel, needle-like rutile crystals or hollow tubes within the stone. Cat’s eye inclusions are aligned parallel to the crystallographic axis and the stones are always cut as cabochons with the fibrous need-like inclusions running across the narrow part of the stone as this is the best way to display the eye.

The most valuable type of cat’s eyes is the alexandrite cat’s eyes where the stone displays both a cat’s eye and a strong colour change. Other kinds of stones like tourmaline, quartz (tiger eye), sillimanite, scapolite, apatite and beryl may also display chatoyancy but these stones are referred to as tourmaline cat’s eyes or quartz cat’s eyes etc., and only chrysoberyl is referred to as “cat’s eye” with no other designation.





May 27, 2020

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