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Gem Lingo - An A To Z of Common Jewellery Terms

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Whether you’re new to gemstones or have been collecting for some time, there are many industry-specific words for which you might not yet know the meanings. To help deepen your understanding of this fascinating trade, we’ve listed some of the more common ones here. There are more in-depth scientific explanations for many of these words, but we’ve kept things simple here, for the benefit of those learning these words for the very first time.


‘Adamantine’ means ‘Diamond-like’, especially when talking about gemstone lustre. It comes from the Ancient Greek word ‘Adamas’ which meant ‘Diamond’.


A shimmering play of colour that appears to be trapped just under the surface of the stone in gems such as Moonstone. Also known as Labradorescence when observed in Labradorite.


Gemstones coloured by their impurities. Sapphire, Tourmaline and Quartz, among others, are allochromatic because they exist in pure colourless form but are also given colour by various impurities. Quartz coloured by Iron gives us Amethyst, for example.


Chemical elements can sometimes exist in several different forms. The chemical formula for graphite and Diamond is ‘C’ because they are both allotropes of carbon. We only set one of them into jewellery, however!


A metal made from two or more other metals. Pure 24-karat gold is too soft for jewellery, so is mixed with other metals to strengthen it. White gold is created by adding silver or palladium to yellow gold, and rose gold is made by adding copper. They are all alloys.


Most gemstones have a crystal structure, but those that don’t are known as amorphous gems. Amber and Opal are good examples.


A gem phenomenon exhibited by few stones that causes a bright star to be displayed across the surface of the gem. Sapphire and Ruby are two stones that can occasionally show asterism.



A phenomenon whereby many small, shiny inclusions within a gem cause the stone to look as though it is glittering.


When a beam of light enters a gem and is split into its colours, we call it refraction or fire. Some gems can split each beam of light twice, such as Sphene. This is known as double refraction or birefringence.


Light reflected out of a gemstone from within, as opposed to surface reflection, which is known as lustre.


Some gemstones aren’t cut with flat surfaces but are instead polished into a dome shape. This is known as a cabochon gemstone. It is often used for gems that show asterism or chatoyancy.



The weight of a gemstone is measured in carats. One carat is equivalent to 0.20 grams, so five carats is equal to a gram.


The name of the phenomenon where a beam of light can be seen across the surface of a gemstone. It is similar to asterism but with just one line. It is also known as the ‘cat’s eye’ effect.


The measure of how clear a gemstone is. It is often dependent on how many inclusions are found within the stone.


In the same way that wood splits more easily if you cut with the grain, gemstones have a cleavage plane that can make them very difficult to facet.

Colour Change

Some gems display a shift in their hue between daylight and candlelight or ultraviolet light. It is a very rare phenomenon seen in Alexandrite, Csarite® and very few others.


The top part of a faceted gemstone, leading from the table down to the girdle.


Crystal Structure

Almost all gems fall into one of seven crystal structure patterns, which is the pattern in which their atoms bond as the gemstone forms.

Crystal Structure


The very tip of a cut gemstone - the pointy end, if you will - is known as the culet.



Gemstones can be cut in several different ways to best show them off. One of the most popular is the Round Brilliant Cut. Antique Cushion Cut and Marquise Cut stones are other examples.



The process of taking the raw gemstone and adding the facets. Cutting a gemstone is known as the art of lapidary, and the skilled person who cuts the gem is the lapidarist.


Not the same as clarity, diaphaneity is the measure of gemstones transparency. Gems can either be transparent, translucent or opaque, like Diamond, Rose Quartz and Turquoise respectively.


When gemstones show two differing hues at different angles, they are known as dichroic. If there are three hues, the term is trichroic.

Eye Clean

Gems may have microscopic inclusions that are not visible to the human eye. In this case, a gem is known as being eye-clean.


Most finished gemstones are made up of many flat surfaces arranged in a certain way to bring the best qualities out of a gemstone. Each flat surface is known as a facet.


Gemstones often belong to families. For example, the Beryl family includes Emerald, Morganite and Aquamarine. Ruby and Sapphire belong to the Corundum family. Amethyst and Citrine are both Quartz family members.


Another word to describe the refraction of white light into a rainbow of colours when it enters a gemstone.



Some gemstones appear to hold a glow, such as Fluorite and Apatite. This phenomenon is known as fluorescence.

Generational Gemstone

A stone that is discovered and thoroughly mined out during the lifetime of one generation of people. Tanzanite is one such stone unless a new deposit is ever found.


Some gemstones form in geodes, hollow rocks that provide the perfect environment in which a gem can form.


The widest part of a cut gemstone is known as the girdle.



A rare and very popular metal into which gemstones are often set for jewellery. It can come in different purities, such as 9-karat and 18-karat.


The consumer protection scheme that ensures you get what you pay for when you buy precious metals such as gold, silver and platinum. Each piece, as long as it is above a certain weight, is stamped with a hallmark at one of the four UK assay offices. For example, 9-karat gold is stamped ‘375’, as it is 37.5% pure gold. Hallmarks also feature a mark for the office that stamped them, the jeweller that created the piece and often a date letter too.



Gemstones are measured in their hardness on the Mohs scale of one to 10, where one is the softest and 10 is the hardest: the harder, the better for gemstones you’ll wear frequently. For example, Diamond measures 10, Ruby and Sapphire nine, Emerald eight and Amethyst seven.


The colour of a gemstone can be broken down into hue, tone and saturation. Hue is the word to describe what we would traditionally call its colour - red, green, yellow, etc.



Idiochromatic gemstones get their colour from their inherent chemical composition. In other words, the stone cannot exist in any other colour. Peridot is a popular example. The opposite of allochromatic.


Inclusions are small foreign objects or minerals that have been trapped inside a gemstone while forming. Far from being a bad thing, they can give each gemstone a unique appearance. We often call them the fingerprints of Mother Nature.



When you see a rainbow of shifting colours on the surface of soap bubbles, this is iridescence, and it occurs in gems too. Opal, Ammolite, Pearl, Mother of Pearl, Moonstone and Labradorite are all iridescent. Sometimes the word is tweaked for the individual gemstone, such as opalescence for Opal, pearlescence for Pearl and labradorescence for Labradorite.


Not to be confused with carat, which is a weight, karat is a measure of gold purity. Pure gold is known as 24-karat, while 18-karat gold is 75% pure, and 9-karat gold is 37.5% pure.


A small magnifier that jewellers and collectors use to get a closer look at gemstones and jewellery. Also useful for reading any hallmarks on your pieces.


Loupe Clean

A gemstone that appears free of inclusions, not just to the naked eye but also at 10x magnification under a jewellers loupe.


Any reflection of light bouncing back off the surface of a gemstone, as opposed to having entered the gem and bounced back from inside, is called lustre.


Gemstones need to be found, and we do this by mining. The mine may be alluvial, such as panning in rivers or exploring dried up riverbeds for gemstones that have been washed from their source by water. It may be open-pit, which is essentially a giant hole (which can still get quite deep and vast) where the removed soil is sifted for gems. It could also be an underground mine in the more traditional sense of a vertical shaft that has horizontal tunnels radiating out from it. These tunnels are then explored for gemstones.


Some gems such as Pearl, Amber and Coral are created organically, and as such, they don’t feature an organised crystal structure like most other gemstones.


Where your gemstone came from. Origin can affect the value of the gemstone, such as with Sapphire from Sri Lanka or Emerald from Colombia.



Gemstones are often traded in parcels, small packages of stones that may have already been faceted. Parcels quite often contain similarly sized and coloured stones.


The bottom part of a faceted gemstone, leading from the girdle to the culet.



Some gemstones, such as Kunzite, can absorb daylight and then appear to be still glowing once taken out of daylight. This phenomenon is known as phosphorescence.


A scarce and expensive precious metal used to set only the very finest gemstones in. It has been theorised that all the platinum ever mined would fit inside the average size living room.


A gemstone that can show differing hues through different axes. A catch-all term for dichroic and trichroic gemstones.

Precious Gems

Traditionally, only Diamond, Ruby, Emerald and Sapphire have been considered precious, while all other gemstones have been categorised as semi-precious. As gemstones have come to be better understood in recent times, this practice has started to fall out of favour.


Before a gemstone is cut and polished into its final form, it is known as a rough gemstone.


When talking about the colour of a gemstone, we use the word saturation to describe how much of the hue there is. Think about butter next to a high-visibility vest. They’re both yellow, but the vest has much more saturation of colour — the same with a strawberry milkshake and a freshly picked strawberry.



Describes the lustre - often bronze in hue - of gemstones that show iridescence such as Labradorite and Moonstone.


This is the sparkle a gemstone often shows when moved around, a word often used to describe the combined effect of fire, lustre and brilliance.


Gems can be set into jewellery in many ways, with some of the most popular methods being claw set, bezel set and invisible set gemstones.



Another popular and rare jewellery metal, which is generally more affordable than gold. We make our jewellery using sterling silver, which is used across the jewellery industry and is 92.5% pure silver. The remaining 7.5% is made up of other metals to add extra strength.


After gemstones have been mined, they are sorted into different groups depending on clarity, colour and many other factors. Colour matching is an essential step in ensuring your finished jewellery piece looks consistent.



It all begins with gemstone sourcing. Many of the world’s mines are located in the very remotest of places. It is up to skilled gem hunters to find where the latest discoveries and most exciting new gems are being sourced.

Specific Gravity

Different gemstones of identical sizes weigh different amounts due to their varying density. This is referred to as their specific gravity and is measured against a control substance, which is usually water at 4 degrees Celsius. The specific gravity of Amethyst is 2.65, meaning that it weighs 2.65 times more than the same volume of water.


The top, flat facet of a gemstone - often the largest single facet of the stone - is known as the table.



Think of tone as a scale between black and colourless. Most Amethyst varieties feature roughly the same hue and saturation, but their tone can vary wildly. Moroccan Amethyst features a very dark tone, while Zambian Amethyst is much lighter in tone.



Different to hardness, which relates to the scratch resistance of a stone, toughness describes its ability to withstand mechanical shock, such as if the stone were to be hit with a hammer. In this case, Jade is the toughest gemstone.


The technical term for gemstone transparency is diaphaneity, as already discussed. Gemstones all fall into one of three categories in this regard - transparent, translucent or opaque. These three classifications are defined thus. Transparent gems allow light to enter and exit the stone mostly uninterrupted. Translucent stones let light enter and exit again, but the light is distorted, diffused or otherwise interrupted on the way through - these gems are often described as cloudy or included. Opaque stones let no light in, with 100% of the light bouncing off the surface of the gemstone.


Natural gemstones are sometimes enhanced using several different methods. Some of these treatments are almost as ancient as the gems themselves, while some have come about more recently. Conventional treatments include oiling, which is common in Emeralds, heating, which helps improve and stabilise colour in many stones, and filling, which enhances the clarity and strength of Ruby, among others. We always disclose treatments here at Gemporia - full details can be found here.


Sometimes when gemstone crystals are forming, gemstone twinning can occur. This is when two gem crystals - sometimes more - intersect each other, creating beautiful symmetrical shapes and unusual natural patterns. It can often look like the crystals have grown through each other, yet their natural crystal structure hasn’t been hindered at all. Twinned crystals are scarce and collectable.



Regardless of how many pieces of jewellery you own, it is always worth having your collection independently valued for insurance purposes.


A type of gold plating that requires the coating of gold to be at least 1.5 microns thick. This helps the plating last much longer than other methods. Usually applied to sterling silver, the process is a great way to get the look of gold without the price.


In simple terms, a Xenolith is a rock that formed far under the ground and was then pushed closer to the surface. This occurred typically when magma from deep in the earth forced the rocks closer to the surface and then solidified around it. These rocks within rocks often contain gemstone crystals. Without xenoliths, we would have very few Spinel, Chrome Diopside or Garnet gemstones as these stones and others formed deeper than we are currently able to mine.

If you'd like to learn more about the locations, science and history behind our gemstones, head over to the explore section of our blog by clicking the button below.


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