Everything You Need to Know About Different Alexandrite Colours
With its mesmerizing colour-changing ability, alexandrite has captured the hearts of gem enthusiasts for centuries. Requiring specific geological conditions to form, any alexandrite stone larger than one carat is considered highly valuable (the largest and arguably most famous alexandrite specimen ever found, housed in The Smithsonian, weighs over 65 carats!). Below, we’ll examine alexandrite stone colours and the fascinating science behind its iconic colour change phenomenon.
What’s alexandrite stone?
Alexandrite is a variety of chrysoberyl, a mineral formed from the mineral beryllium aluminium oxide. The name ‘alexandrite’ specifically refers to the type of chrysoberyl that demonstrates colour change under varying light conditions. (Other chrysoberyl varieties include ordinary yellowish-green chrysoberyl and cymophane, also called “cat’s eye”.)
This seemingly supernatural gemstone type was first discovered in the Ural Mountains of Western Russia in the 1830s. It was named after Czar Alexander II, who was Emperor of Russia at the time, quickly becoming popular among the country’s aristocracy.
The June birthstone forms when beryllium and aluminium combine with titanium, iron, and chromium. If just one more element is present, that is, silica, the stone that develops is an emerald. Because the Earth’s crust is made up of 59% silica, making silicon the second-most common element in the layer, chrysoberyl is considered among the rarest gemstones in the gem world.
What is alexandrite colour change?
Alexandrite colour change is the stone’s marvellous ability to appear to change hue under different light sources. Under candlelight or incandescent light, alexandrite appears red, pink, or purple. Under sunlight, alexandrite appears green or blue.
The difference occurs due to the absorption of different wavelengths in these varying light conditions. In the rare blend of chemical elements that make up alexandrite, the single element that makes colour change possible is chromium.
While the proportion of certain elements in alexandrite cause variations in the warmth or coolness of colours and the extent of colour change, it is more accurate to say that any one alexandrite stone is capable of exhibiting up to seven different colours depending on what light shines on it. The more dramatic the colour change in an alexandrite stone, the pricier it is.
Alexandrite is not the only gemstone known to exhibit colour change, but it is the most commonly known gemstone to do so. Other gems that colour change are garnet, spinel, diaspore, zultanite, and fluorite.
What are the different alexandrite colours?
As mentioned, a single alexandrite can exhibit up to seven hues under varying light sources. However, alexandrite gems from different mining locations are unique, displaying different hue strengths; alexandrite colour change can range anywhere from 30% to 100% in strength of effect. Stones that show a pure, vivid red under daylight and green under artificial light, as well as more distinct colour change, are the most valuable. These are called ‘fine-quality’ alexandrites.
Below, we will explain under what conditions each alexandrite colour shows up and how sought-after they are.
The finest alexandrites exhibit a limpid near-navy blue when sunlight shines through them; hints of blue can also appear under fluorescent light. The blue hue of alexandite stone is attributed to the presence of iron. In particular, alexandrites mined in India are known for their vibrant blue-green hue and exceptional transparency.
The most desired alexandrite stone colour under daylight, the most expensive alexandrites can be moss green, teal green, or cool mint green with natural light transmission. In the absence of bright natural light, fluorescent light or a 5000K light bulb that imitates bright, white natural light are both optimal ways to observe the green in an alexandrite.
Often described as a warm, inviting yellow, alexandrite can appear golden yellow under incandescent light bulbs. For those on the market for alexandrite jewellery, it’s important to note that alexandrite that shows up as yellowish-green in natural light and brownish-red in artificial light is much cheaper than red-to-green colour change alexandrite.
Another possible alexandrite colour is pink, which shows up true pink or purplish-pink (think Barbie pink). This hue shows up when the stone is exposed to incandescent light. For instance, the Whitney Alexandrite sourced from Brazil is an unmatched specimen with two main characteristics: high quality and colour-change from blue to rich purple-pink.
With incandescent or even the glow from a candle transmitting through the stone, alexandrite can appear purplish-red (also called ‘plum red’) or purple. This hue can lean toward deep eggplant or ‘royal’ purple to an elegant lavender.
While stated above that alexandrite that conveys a strong red in incandescent light is desirable, in practice, this red is usually purplish- or brownish-red. A true red alexandrite showing up under a lamp or candle is rare to see. To see how much red is really in an alexandrite stone, you can also view it in ultraviolet light.
Grey alexandrite is more accurately described as alexandrite with weak or limited colour change. Alexandrite stones with a lower percentage of colour change, at or near 30% (chrysoberyl with a colour change of less than 30% is not classified as alexandrite), has a grey cast or grey areas throughout the stone under artificial light. This hue can be light, dusty purplish-grey or a mysterious cloudy bluish-grey. Grey is one of the least-desired alexandrite stone colours, since it effectively inhibits the colour change effect.
As mentioned, alexandrite is fairly rare in natural Earth environments, especially those larger than two to three carats. However, since the 1900s, processes like the Czochralski technique and melt process have been fine-tuned to create synthetic alexandrite in a lab environment. These ethically manufactured stones have fewer inclusions and in the most in-demand colours on the market, without any of the conflicts related to gemstone mining. The end result is also much more affordable than mined alexandrite.
Inter-Pacific Holdings Ltd. sources and produces seven types of ethical lab-grown gemstones and presents them to the market under the BIRON® brand. Get in touch for a complimentary consultation to see how our sourcing, cutting, and polishing services can help your business.