Alexandrite vs Diasporite: Comparing Top Two Color Change Gemstones

In the world of colour change gemstones, there are a number of key players who are battling it out for the top spot, which is a niche market. In addition to certain popular gemstone types like corundum stones that can produce such colour change effects at various levels, there are a handful of top gemstone variants which are renowned for showcasing this effect. One of the most prominent gemstones in the colour change range of gems is the alexandrite: a variant in the chrysoberyl family, that is known to produce two contrasting colours, a distinct bluish shaded green under sunlight, to a raspberry red under incandescent light. Alexandrite gems have built a global reputation for their rarity, high durability, and importantly their ability to colour change.

The ability of natural gemstones to generate this effect has made it sought after feature, as gemologists, top jewellery buyers, and gemstone enthusiasts are on the lookout for the next top colour change gemstone. Part of this interest is driven by the rarity of gems that have this feature, and the high prices that they are able to command in the fine jewellery market. Here we will analyse a new addition to the colour change gemstone: Diasporite, also known as the diaspore. These gems are sometimes referred to by their trade names: Zultanite, and Csarite. In this post, we will compare and contrast the main differences between alexandrite and diaspore gems, which are among the top colour change gems in the world. In the process of doing so, we will provide a quick but informative overview of their key features to help decide between the two.

What are Diasporite Gemstones?

Diasporite or diaspore as it is commonly known is a variant in the aluminium hydroxide oxide AlO(OH) group of minerals, that is sourced from a handful of countries, with Turkey (formerly Anatolia) being the primary source today. Diasporite gems are sourced from metamorphosed limestone and bauxite deposits: the latter which is a sedimentary collection of rocks that is known for its high aluminium content. Diasporite gems come in a range of colours, with the most dominant hues being: pink, pale green, rare variants of purple, and the most popular hue, one that is most sought after in the gemstone industry: yellow. Yellow cut diasporite gemstones that can shift colour from yellowish-green under daylight to orangish pink under incandescent light.

Geology and Origins

The origins of diasporite gems go back to the start of the 19^th century, however, they only entered popular use in the 1970s, with their colour-changing feature gaining greater recognition. However, things only started to take around the mid-2000s (2006) which is when gems entered the commercial adoption. A key selling point of these gems is their rarity. Whilst diasporite gems are found in various parts of the world, actual gem-quality stones are much rarer, with the most notable source being sourced from the Anatolian mountains in the central uplands of Turkey. The regions that make up Western and South Western Turkey, notably the city of Milas in Muğla Province were a historical source of large diasporite stones. As these gems are sourced from the region that used to be the home of the former Ottoman empire, they have been associated as the gems of the Sultan: hence their other name Zultanite. One of the issues with diasporite gems is that a majority (around 60 per cent), are predominantly opaque in character, with the colour gem variety making the smaller portion. In addition to their colour change feature, which is not uniform across all gems in this range, a lot of diasporite gems are found in a soil-brown tone, which is not desirable, thus increasing the competition for the olivine, yellow stones.

Colour Change Effect in Diasporite Gemstones

The key feature in diasporite the gem one is its colour-changing feature. Under sunlight and fluorescent light, good quality diaspore gems will produce a yellowish-green in some instances an olive-green tone. And under incandescent light, or light produced by fire, these stones are known to shine with a hue that is closer to the raspberry red. The latter is interestingly one of the hues that are displayed by alexandrite gems when viewed under the same lighting conditions. With respect to the chemical character of the stone, diasporite gems primarily consist of aluminium oxide, combined with lower but significant levels of hydrogen. These stones, like many in the gem world, contain various levels of trace elements that are responsible for their colour (also known as chromophores). An array of them, including iron, magnesium, titanium and chromium. Diasporite gem-quality stones have only begun to penetrate the market for fine jewellery, this is due to a number of factors, one of which is the rarity of gem-quality stones, but also their relatively lower durability: with diasporite gems only scoring a 6.5 – 7 in the Mohs scale for hardness. However, they are nonetheless pursued as a niche gemstone category, with growing enthusiasm from colour change gemstone seekers.

How do Diasporite Stones Contrast with Alexandrite Gems?

When studying the differences between these two colour change gemstones, the question you have to ask is what are you primarily looking for? Often gemologists, gem enthusiasts, jewellery companies, gem merchants and fine jewellery buyers seek gemstones for a variety of reasons. All of which no doubt have a point of convergence, but they do differ with respect to their primary aims. Since this is a discussion about colour change gemstones, this particular feature ought to be the main concern. When it comes to picking between two colour change gemstones the first point of concern is the colour of the gem when viewed under a certain lighting condition. With alexandrite gems, which alternate between green to green-blue or red to raspberry red, depending on the nature of the light source. With diasporite gems however the colour character is more variable, as gemstones in this range are found in a spectrum of hues that fall between yellow, light brown, and green to colourless. With the key colour change corresponding to the movement from a greenish-yellow to a pink or orangish pink hue. However, this shift in colour is greatly dependent on the character of the stone, as colourless and certain greenish-blue variants of the diasporite stone may not feature the colour change effect.

Rarity

The next feature that affects the selection criterion for gemstone buyers is the rarity of the precious stone. Alexandrites are among the rarest gemstones in the world, rarer than diamonds and even rubies. This is due to their rare mineral combination: as an aluminate that contains beryllium, along with the presence of chromium (that contributes to its colour) is extremely rare in the natural world; and combined with the stone’s high durability makes it a much after option, especially when combined with its colour change feature. With gem-quality alexandrites being sourced only from a handful of countries around the world. With diasporite stones however things are a bit different, as the supply of these stones is somewhat greater, though gem-quality stones, particularly those which can produce the distinct yellow-pink colour change effect are rarer. Thus if one is in the market for a gem-quality diasporite one is best to seek out gems mined from parts of Turkey, which are rarer and more competitive.

Suitability for Engagement Rings

In the world of fine jewellery, engagement rings dominate, and picking a top-quality gemstone that can stand out from the rest is a key point many ring buyers look for. When it comes to choosing between the alexandrite and diasporite gemstones, a number of factors come into play. Two factors we have already engaged in: the distinctiveness of the colour change effect, and the gemstone’s rarity. On these two factors alone alexandrite gems are at an advantage. Since the colour transition that is considered acceptable in alexandrite gems is fixed: with blue-green colour shifting to the raspberry red tone depending on the lighting condition being the top choice, gemstones in this range fall short of this standard are considered an inferior type. So the range of choices for this gemstone whilst limited, helps buyers choose between a set combination.

Diasporite is a mixed bag in that its colour change effect is not as pronounced and uniform as alexandrite stones, given the various hues with which gemstones in this range are found.  And the measurement of colour change for diasporite is still being studied by experts and gemologists given their relative newness. So potential customers might have to do greater research in seeking a quality stone, with the Turkish variants being the best option. So when combining these factors with gemstone durability, which is a key factor for fine jewellery making like engagement rings, alexandrite remains a better choice, albeit a pricer one. But the market for diasporite is still evolving and in time we will tell if they rise higher.