The Garnet family of minerals encompass a wide range of fascinating and beautiful, varieties and colours. The colour most often used in jewellery is reddish-brown and these stones are often used as a cheaper alternative to Rubies. The name itself, Garnet, comes from the old English word ‘gernet’ which means dark red. There are, however, varieties of garnet that are very valuable gemstones in their own right and in our opinion some of the most interesting and attractive of these are green garnets.
Garnets measure from 6.5 - 7.5 on the Mohs scale of mineral hardness and each variety measures slightly differently. All of the varieties that contain green garnet measure from between 6.5 - 7.5. Like colour, it is the chemical make up of these garnets that account for the variation in hardness. Garnets that contain calcium will typically have a lower hardness than those that contain iron. (geology.com). This measurement indicates that garnets are great for all types of jewellery, including earrings, necklaces, and bracelets, with the exception of rings.
In this article, we take a look at the green varieties of garnet, what gives them their colour, when and where they were discovered and how they are used in jewellery today.
Image by Lina Jakaitie, strike-dip.com
What Are Green Garnets?
‘Garnet’ is actually a term given to a group of closely related minerals. Differences in the exact chemical structure of these minerals, gives them their distinct colour. In the case of garnets, this can be a single mineral, such as chromium or a combination of chemical elements.
The diagram above demonstrates beautifully how various chemical inclusions affect the colour of garnets. The 3 green varieties of green garnet are known as Andradite, Grossular and Uvarovite though these names are used by gemmologists and may not be familiar to most jewellery lovers.
The exact chemical composition of the stone determines which type of garnet it is. These scientific categories correlate somewhat with the varieties listed below though there is some overlap as we are looking at the ‘trade names’ of the stone. As well as the chemical composition, the location and colour or hue of the stone can help to determine what ‘type’ of green garnet it is.
Tsavorite Garnet
This type of garnet is very rare and was only discovered in 1967, by the late British geologist Campbell Bridges. The initial discovery was made in Lemshuku, northern Tanzania. Bridges later found a deposit in the Tsavo National park in Kenya and it is after this park that the stone is named. Since then, more deposits have been found in neighbouring Tanzania & Madagascar but are still known as ‘Tsavorites’ in the jewellery trade.
Tsavorite’s are a type of grossular garnet and its trace amounts of vanadium or chromium that give them their colour. The colour of Tsavorites can range from a relatively light, minty green to an intense bright green similar to that of high-quality emeralds.
Various shades of Tsavorite garnet
It is very rare to find large Tsavorite crystals. Most finished gemstones weigh less than 2ct. and stones larger than 3cts can command very high prices. The largest Tsavorite ever cut weighs 325.13ct and was found in Tanzania. Tsavorites were associated with American Jewellers Tiffany's who launched a marketing campaign to promote the then little known stone in 1974. Since then many other jewellery houses have used the gemstone in designs and jewellery containing Tsavorites are popular at auctions.
A demantoid garnet from Namibia
Demantoid Garnet
A super sparkly gemstone, originally discovered in Russia’s Ural mountains, the name ‘Demantoid’ literally means, like a diamond. The exact colour of Demantoid garnets differs depending on which location they are found in and they can have inclusions which actually make them more valuable.
Demantoids are a variety of Andradite garnet and chromium is again the cause of the stones green colouration, whilst Ferric iron is the cause of yellow in the stone. Variations in the exact chemical composition account for the variations in colour.
Stones from Russia, where they were originally discovered generally have the best colour, though in 2003 it became known that they were regularly subject to heat-treatment to enhance their colour.
Namibian stones are known to be lighter in colour, with more yellow and brown tones but this means they have a superior sparkle.
Demantoids from Russia still command the highest prices and some contain what is known as a horsetail inclusion. These inclusions resemble a horses tail and are also found in demantoids from Italy and Iran but not from Namibia or Madagascar.
Meralani Mint Garnets
The most recent addition to the list of garnet varieties of garnet, this lighter shade of grossular garnet is named after the locality in which it is found, Merelani, in Northern Tanzania. It is very similar to Tsavorite garnet but lighter in colour. The Tsavo national park is just 100 or so KM away and in the past, these stones would likely have been described as Tsavorites.
Given the consistent differences in colour in stones from the Merelani area, it has become helpful to create a distinct product group.
Green garnets being traded in Meralani, Northern Tanzania.