Color Change Gemstones

The famous London jeweler, Edwin Streeter, described the color-change Alexandrite gemstone as ‘an emerald by day and an amethyst by night’.

Color-changing gemstones captivate jewelry enthusiasts with their mesmerizing ability to shift hues under different lighting conditions, offering a dynamic and enchanting visual experience. These unique gems, such as alexandrite and sapphire, exhibit a phenomenon known as the "color-change effect," where their appearance transforms based on the light source. Outside, in normal daylight, the gems may look green, blue, yellow or whatever color it may be then as soon as it is taken indoors it will change color to red, orange, purple or any one of a myriad of colors. It is almost magical.

There are a few gemstones with this color-change ability including color-change sapphire, color-change garnet, color-change diaspore and, most famously, alexandrite. All with subtle differences in color and in their ability to change not only in different sources of light but also at different times of the day!

But how does this happen?

A quick science lesson. Imagine you are looking at a red apple. What we see when we look at an object is reflected light (this is a very general science lesson) so waves of all colors hit the apple and all the colors are absorbed by the apple except red which reflects back so the apple looks red.

Different light settings can affect what colors we see. For example a blue sapphire viewed by candle light will look different to one seen in sunlight. Candle light is rich in red wavelengths but poor in blue wavelengths so when you look at the sapphire under candle light it looks almost black because no blue wavelengths are there to be reflected.

Experienced gem dealers know exactly what lights are best for their gemstones even down to the time of day and direction of the sun. The same effects are used to make our faces look good in restaurants and vegetables look delicious in supermarkets.

Daylight contains more blue and green light and less red light, incandescent light has more red light and less blue and green light. In addition the temperature of the air around us also affects the light, cool mornings show up blues better than warm afternoons which make gemstones look redder.

These lighting conditions affect everything we see from fruit to leaves to gemstones, and the chemical make-up of each object will also contribute to its color. Rubies are the red form of the mineral corundum, corundum is aluminum and oxygen and is colorless unless minute impurities are added. In the case of rubies, traces of chromium replace the aluminum. The chromium atoms absorb the all the light except red and this is what give rubies their deep red colors.

Other minute chemical variations cause the different colors in color-change gemstones, usually chromium or vanadium. Exactly how this phenomenon occurs at this atomic level is not known but the angles of the crystals, rutile inclusions and infinitesimal deviations in chemical structure will play a part.

Enough science, how about the gemstones? The most famous color-change gemstone is Alexandrite, discovered in the Ural Mountains of Russia, and named after the future Tsar Alexander II. Its discovery in Russia and being red and green, the same colors as the Russian army uniforms, cemented its association with this country. 

Alexandrite is a type of chrysoberyl and is one of the most valuable gemstones in the world. It is very difficult to find any Alexandrite from Russia anymore and almost impossible to find anywhere else.

In 1987, Alexandrite was discovered in a valley in Brazil, within weeks 3000 miners had descended upon a ridge barely 200 meters long and begun to dig. On average, a person a week was shot in a dispute over mining rights and, in the four months before the mine was exhausted, it is estimated that two hundred and fifty thousand rough carats (50kgs) were extracted.

Garnets exhibit possibly the widest variety of colors among the world’s gemstones and its color-change variety is one of the most attractive. Changes from pale yellow to deep orange and rich honey to golden brown are all possible in this exquisite example. It is never treated as far as we are aware and comes in large, clear gemstones in all manner of cuts and facets.

Color-change Diaspore is another lovely gemstone which is a kiwi green in natural light and switches to a champagne yellow under incandescent lighting. A third color can be seen in candle light when the gemstone takes on a pinkish glow. Its name come from the Greek ‘to scatter’ because of its sparkling appearance. High quality color-change Diaspore can be found in a single location in Turkey and is marketed under the name Zultanite or Csarite.

One of the most valued and sought after color-change gemstones is the Sapphire. They are usually very clear gemstones and are most often found in smaller sizes and facet cut to maximize the color shift. As with most sapphires, color-change gemstones are heat-treated to enhance their look.

Color-change Fluorite is quite a soft gemstone so should be reserved for pendants, necklaces or brooches when used as jewelry or just kept as a fascinating loose gem. Its intense color change is a wonderful phenomenon well worth seeing as it changes from blue to purple in dramatic fashion. This usually untreated gemstone comes in lovely large sizes and creative faceted cuts to really display its beauty.

A relatively new arrival to the world of color-change gemstones is Hyalite Opal and what an impressive debut. Hyalite Opals are usually clear, colorless or just slightly yellow under normal lighting but under UV lights or sunlight they glow a dramatic deep green color. In Hyalite Opal’s case this color change is known as fluorescence. Fluorescent items shine up instantly when hit by UV light – it is almost unbelievable to see in action.

The one other color-change gemstone we are aware of is Andesine which comes from Congo, China and Tibet which supposedly changes from deep green to bright purple but it is very rare and may be of dubious origins so we will reserve judgment until we have seen one ourselves. 

And that is it, just the six varieties of gemstone with an appearance so rare that they are referred to ‘Phenomenal Gems’. Each gemstone is an uncommon object of beauty even in just the single color and they take a magical leap with this extraordinary ability.