Glorious garnet shows off its nuance

by Samantha Ashenhurst | August 18, 2023 10:54 am

By Lauriane Lognay

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My follow gemmologists, I ask you: Is there a group of gemstones more intriguing and complex than garnets? This gem represents such a significant part of our industry. With more than 20 categories, garnet is, indeed, a wonderous and diverse stone.

The term “garnet” comes from the Latin word granatum, meaning pomegranate. This monicker is due to the gem’s resemblance (in its rough shape) to the seed of the fruit. Though most often represented in its classical variety—the pyrope or almandine-red colour—garnet exists in a variety of hues. What’s more, it is also available in a range of prices!

Additionally, contrary to the diamond, the corundum, or even the tourmaline, garnet doesn’t have a family. Rather, it belongs to a “group” for a very peculiar reason.

What do we know?

A familiar gem in the market, garnet is known for its red colour and affordability. It is also January’s birthstone.

Garnet is a popular choice because, apart from some heating (and even that is rare), the gemstone is never treated, and doesn’t need to be. It is often found in large sizes and is, overall, quite a pure stone. Further, it does not have any well-known synthetics, apart from yttrium aluminum garnet (YAG), which is rarely seen.

Garnet has a hardness of 6.5 to 7.5 on the Mohs scale, depending on the variety, which means it is a solid gem to set in any jewellery type.¹ Additionally, it can be found almost anywhere in the world, with no shortage in sight. Flawless gems in large sizes are recovered fairly easily.

As an added bonus, garnet also displays several interesting phenomena, including four- to six-ray asterisms, some colour change, and, in rare cases, cat’s eye.²

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Family versus group

Before addressing how garnet, itself, is classified, let’s first discuss the distinction between a gemstone “family” and a “group.”

Simply put, gems from the same family have the same chemical composition. The element that colours the stone does not change its composition because the quantity in it is too minute or, otherwise, an integral part of the chemical composition. A good example here would be corundum (red ruby versus blue or green sapphire).

A group, however, represents gemstones of similar chemical composition as a starting point (also within the same crystalline system, among other things), but this is influenced by the colouring element inside the stone. With this in mind, garnets are, in a way, cousins, whereas tourmalines are siblings. Likewise, feldspar is considered a group and not a family.

Breaking it down, for corundum (i.e. a family):

• A green sapphire has the chemical composition of Al₂O₃
• The red ruby has the same: Al₂O₃

For garnet (i.e. a group):

• Green garnet (tsavorite) has the chemical composition Ca₃Al₂(SiO₄)₃
• Orange garnet (spessartite): Mn²⁺Al₂(SiO₄)₃

This makes the garnet a rather complex group of gems for consumers who, perhaps, are not familiar with them. Each variety has its own quirks: Some are magnetic, some don’t react well to the polariscop, some do not have the same hardness of refractive index, and some do not have the same inclusions.

On the gemmologist side of things, to be well versed in identifying garnets, one has to know them all.

It’s in the detail

Garnet is divided into two major categories: The aluminum series (pyralspite) and the calcic series (ugrandite), with each presenting different primary colours.

Pyralspite series:

 

• Almandine (red to orange)
• Pyrope (red)
• Spessartite (orange to red, also called “mandarin garnet” on the market)

This series includes the rhodolite garnet (purple—a mix of the almandine and pyrope) and the Malaya garnet (orange to red-orange—a mix of spessartite and pyrope), amongst others.

Ugrandite series:

 

• Grossularite:

 

• • Hydrogrossular (green)
  • Hessonite (orange to peach)
  • Rosolite (pink)
  • Leuco (colourless)
  • Tsavorite (green)

 

• Andradite:

 

• • Demantoid (green to yellowish brown)
  • Topazolite (yellow)
  • Melanite (black)

 

• Uvarovite (green)

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Worth noting

In addition to the better-known garnets, there are also a few noteworthy varieties often seen on the market, along with several others we don’t see much, but are considered highly valuable for collectors and garnet fans alike.

Colour-change

There are different types of garnets which change colour, with the most common (but less desired) variety being a yellowish to brown colour. Among the more rare and sought-after varieties is the blue-to-raspberry colour. This is particularly hard for collectors to get their hands on today, as there are no new finds.

The rarest and most desired in this category, however, is the blue-to-green garnet.³ This type also has the distinction of being the most recent discovery in this group, having been recovered from a deposit near the border of Tanzania and Kenya in 2017.

Rainbow

Rainbow garnet is often kept rough and almost never cut because of one particularity: It has an iridescent “coating” on its surface, caused by its layered formation. This iridescence disappears once the rough is cut. This type of garnet can be found in Japan or in Mexico and is part of the andradite garnets.

Malaya

The Malaya garnet is well-loved on the market because of its beautiful colour, which ranges from orange to a reddish orange. This stone can sometimes also be colour-change, and the colour is often referred to as “imperial.” Malaya garnet mostly comes from Tanzania and Madagascar.

Dragon

A relatively new variety, the dragon garnet was circulating at the Tucson gem shows this year. While this stone is not yet widely available on the market, interest for it has spiked. This gem, which is a form of Malaya garnet, shows a strong reaction under ultra-violet (UV) light.

Pyrope/Almandine

While pyrope and almandine garnet are technically separate varieties, I am opting to group them together because, on the market, they are essentially considered the same. This is the typical red-brownish or orange-red colour. It is the most well-known garnet and can be found almost anywhere on the planet.

Spessartite

While this garnet variety comes in red, this is not the colour typically seen on the market, as most collectors are after the more traditional (and remarkable) bright orange hue. This type is also called “Fanta,” “mandarin,” and “spessartine.”

Also, if you have an N52 magnet handy, you can have a little fun with spessartite. This gem is one of the only garnet varieties that is magnetic.

Tsavorite

Available in colours ranging from beautiful forest green to more yellowish, Tsavorite garnets exploded on the market in 1960 when they were discovered in large quantities at the border of Kenya and Tanzania (in the Tsavo region). Today, Tsavorite can be found in these regions, as well as in Zambia, Madagascar, and Pakistan.

Demantoid

Found mainly in Russia and Namibia (as well as in Canada in smaller quantities), the demantoid garnet has one of the highest lustres in its group. This variety is famous for its intense emerald-green colour.

Interestingly, contrary to the other types of garnets, the demantoid’s value increases if it has a certain inclusion called a “horsetail inside” of it.⁵ The clearer and better detailed the inclusion is, the higher its potential price.

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A world of colour

The garnet group is certainly a big one—January babies have a vast choice of hues and rarity to choose from! Beyond the scope of colour, garnet keeps on giving with its interesting phenomena and inclusions.

The next time you meet with a client who is looking for a garnet but worries, perhaps, that the gem is “too boring” or common, explain to them the different types that exist. This is, indeed, a robust and surprising gemstone group. While these gemstones can be found all around the globe, it is still possible to find a unique piece that tells its own story.

[5]Lauriane Lognay is a fellow of the Gemmological Association of Great Britain (FGA) and has won several awards. She is a gemstone dealer working with jewellers to help them decide on the best stones for their designs. Lognay is the owner of Rippana, Inc., a Montréal-based company working in coloured gemstone, lapidary, and jewellery services. She can be reached at rippanainfo@gmail.com[6].

References

¹ For more, see “Hardness, tenacity, and stability: The gem world’s trio of durability” by Lauriane Lognay, published in the February 2023 edition of Jewellery Business. Find it online here: https://www.jewellerybusiness.com/gemstonesgemmology/hardness-tenacity-and-stability-the-gem-worlds-trio-of-durability[7]

² For more, see “A gift from nature: The 10 optical phenomena of gemmology” by Lauriane Lognay, published in the July 2021 edition of Jewellery Business. Find it online here: https://www.jewellerybusiness.com/gemstonesgemmology/a-gift-from-nature-the-10-optical-phenomena-of-gemmology[8]

³ For more, see “New horizons: How fresh discoveries push the gemstone industry forward” by Lauriane Lognay, published in the October 2018 edition of Jewellery Business. Find it online here: https://www.jewellerybusiness.com/features/new-horizons-how-fresh-discoveries-push-the-gemstone-industry-forward[9]

⁴ For more, see “Tucson is back!” by Lauriane Lognay, published in the May 2023 edition of Jewellery Business. Find it online here: https://www.jewellerybusiness.com/features/tucson-gem-shows-2023[10]

⁵ For more, see “Inclusions: Are they friend or foe?” by Lauriane Lognay, published in the October 2017 edition of Jewellery Business. Find it online here: https://www.jewellerybusiness.com/features/inclusions-friend-foe[11]

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