Alexandrite Quality Factors
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.
Production from Russian mines is very limited today, which means the intense, fine-coloured gems they produced in quantity less than 200 years ago are much harder to come by.
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.
This colour-change alexandrite has low saturation in both its green and red colours, making it slightly brownish and less desirable. - Alan Jobbins
The colour change displayed by this alexandrite from Sri Lanka lacks strength, and its colours are brownish.
Alexandrites from Brazil have been found in colours that rival the Russian material, but production from Brazil has decreased.Currently, alexandrite supply is low, and fine-colour material is extremely rare.
Clarity
Alexandrite tends to contain few inclusions. There’s a dramatic rise in value for clean material with good colour change and strong colours.
A high clarity rating raises the value of alexandrite, especially one with nice colour change like this green to red-purple example.
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.
Cat’s-eye alexandrite, with beautiful chatoyancy along with colour change, is extremely rare.
CutAlexandrites 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.
This alexandrite has stunning colour change with intense colours, and very clean clarity. It’s an oval mixed cut, which is common for alexandrite. - Courtesy Evan Caplan Fine Gemstones
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.
This 8.82-carat cushion-shaped alexandrite shows nice colour change. Its large size is rare for this stone.
Attractive alexandrites used in jewellery are usually under a carat. This is a 0.65-carat triangular-shaped stone.
