Gemstone Buying Guide

Gemstone

Interest in gemstones, outside of diamonds' perennial popularity, has increased over the past five years. Gemstones come in an endless array of colours, sizes and shapes, making them perfect for every taste and occasion.

Whether looking for the perfect gem for an engagement ring, statement cocktail ring or everyday pendant or earrings, our guide will help inform you about the fascinating world of gemstones.

 

What is a gemstone?

The majority of gemstones are mineral crystals that, when cut and polished, can be used to adorn jewellery. Examples include diamonds, emeralds, sapphires, rubies and tourmalines. However, certain organics also fall under the gemstone category, such as amber, pearls and jet and copal. Although they are not minerals, they can still be cut, polished and used for human adornment.

Minerals and organics are chosen for their beauty, rarity and durability when being used to create pieces of jewellery. For this reason, not all minerals can be gemstones as many will not have aesthetic or economic value. Tastes and fashions change over time, as does the popularity of individual gemstones. Still, the desire for beautiful eye-catching jewellery remains.

 

Gemstone treatments

Coloured gemstones are subjected to a growing range of treatments designed to enhance their value. Heat treatment is routinely used to develop more intense colours in rubies and sapphires while being combined with diffusion treatments designed to fuse colour into the gemstone's surface. Irradiation is sometimes used to enhance the colour of gemstones such as topaz, tourmaline and fancy diamonds. Generally, these treatments are permanent.

Surface cavities that would otherwise reduce the gemstone's value can be filled with glass-like substances, and surface-reaching fractures, fissures and laser drill holes can be repaired with glass and plastic resins. Emeralds are routinely referred to as 'oiled', as coloured coatings are applied to enhance the natural colour's intensity. If a gemstone has been identified as having been treated in this way, then care must be taken in the wearing and cleaning of the jewellery which contains them. Extremes of heat and ultrasonic cleaning are not recommended and detergents may affect coatings.

good gemstone laboratory will look for these treatment signs and include the information on the gemstone report. Some of these treatments can be controversial as they enhance the beauty of gemstones potentially unsuitable for jewellery. It is challenging to find untreated natural gemstones in some categories, which can attract a significant premium.

 

Gemstone classification

Until relatively recently, coloured gemstones were divided into precious and semi-precious categories. However, as some 'semi-precious' stones are scarce and expensive (there is nothing ‘half-precious about them!), this distinction has been abandoned in favour of simply describing them as gemstones. That said, some gemstones do command much higher prices than others. If you are buying significant emeralds, rubies or sapphires, it is sensible to get a gemstone identification report from a gemmological laboratory to identify any fake stones and determine their quality. The report will also identify any treatments which may have been applied to the gemstone.

Some retailers may already have gemstone reports. Several internationally recognised independent laboratories carry out such testing. The Gemological Institute of America (GIA) and The Certified Gemological Laboratory of Europe (CGL) will certify gemstones and provide certification.

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The A-Z of gemstones

Below is a guide to the most popular gemstones found in jewellery and what to look out for when making a purchase.

 

Agate

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Agate is a variety of chalcedony, typically banded with colours from trace metals within the minerals that provide the stone with striking and unique patterns. Its distinctive appearance, toughness and affordability make it ideal for jewellery.

Amazonite

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Used in jewellery for thousands of years, Amazonite is a semi-opaque stone generally with a green hue. Made from the most abundant mineral in the world, microcline feldspar, Amazonite is sometimes called Amazon Jade due to its vivid green colour.

Amber

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Amber is a fossilised tree resin found in various colours but most commonly associated with red, orange and yellow when found in jewellery. Amber is usually found with inclusions and these internal imperfections add to the stone's beauty. Most commercial amber is cut into cabochons.

Amethyst

Birthstone: February

Star sign: Aquarius

Wedding Anniversary: 6th

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Amethyst, a quartz stone, has a long history of use as a gemstone. Quartz forms within volcanic rock. As the molten rock cools and solidifies within the crust, air pockets form permanent voids. Mineral-rich fluids move within the crust and collect within these voids. With time, crystallisation from these fluids occurred, creating the raw quartz.

Amethyst can range from pale violet to a deep reddish-purple. Its name derives from the Greek word amethustos, which translates as ‘not drunk’. Historically amethyst has been kept as a talisman to counteract the effects of alcohol. The rich would often drink from carved amethyst goblets or even add powdered amethyst to their wine to counteract the effects of alcohol. This belief continued for centuries.

The most prized amethysts come from Russian and Siberia. Like many gemstones, amethyst generally falls under an AAAA to B grading system. It is incredibly rare to find amethysts in the top-grade, with most commercial amethyst falling between AAA and AA. Consistent colour is key to achieving a good price for an amethyst stone. A vibrant yet transparent example possesses the best sparkle. Amethyst is an affordable option if you are looking for a large stone. Larger crystals are readily mined, making carat size less of a factor in their price. Due to their abundance, most commercial amethysts are natural. Heat-treating the gemstone will cause it to go yellow. This will sometimes lead to amethyst being wrongly identified as citrine.

Aquamarine (Tivon) 

Aquamarine

Birthstone: March

Wedding Anniversary: 19th

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Aquamarine derives from the mineral beryl and can vary in colour from turquoise to a deep blue. Darker blue examples are more valuable, but lighter blue is typically what consumers look for when purchasing aquamarine. The gemstone has been used in jewellery for centuries and remains a popular choice today. Clarity is a crucial factor in determining value, with most commercial aquamarines being crystal clear. Aquamarine can be cut into most shapes. The emerald cut is particularly popular as it accentuates the gemstone's colour and sparkle. 

Carnelian Monica Vinader 

Carnelian

Birthstone: July

Star sign: Cancer

Wedding Anniversary: 17th

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Carnelian is a red or orange variety of chalcedony and gets its rich colour from iron. The stone once held great value but is now the most inexpensive chalcedony gemstone. It can vary from semi-opaque to translucent in its transparency. Most commercial carnelian comes from India.

Chalcedony  

Chalcedony

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Chalcedony is a variety of quartz. Commercially, chalcedony refers typically to the translucent milky blue and grey stones, but the likes of bloodstone and carnelian are also part of the same family.

Chrysoprase Sushilla Jewellery

Chrysoprase

Birthstone: May

Star sign: Cancer

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Another chalcedony, chrysoprase, gets its vivid green colouration from traces of nickel. The most sought after chrysoprase is apple-green in colour and darker in tone, creating a brightly saturated gemstone. Chrysoprase is popular in carvings and jewellery.

CITRINE  (Ntinga)

Chrysoberyl

Wedding Anniversary: 18th

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Cat's eyes and alexandrite are notable examples of chrysoberyl, a hard stone that appears yellow to brown in colour. Cat's eye chrysoberyl get their name from the chatoyant effect in the stone. This refers to a band of bright lustre caused by reflections from the stone's inclusions giving the distinct banded division. Alexandrite is chrysoberyl that changes colour. Most chrysoberyl is cut into cabochons.

Citrine

Birthstone: November

Wedding Anniversary: 13th

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Citrine is a rare yellow quartz and can be found in various tones, from gold to pale yellow. A cousin to amethyst, citrine is a popular gemstone thanks to its beautiful colour, durability and affordability. Most stones are heat-treated to give them a distinctive yellow colour. Thanks to its warm autumnal tones, it has become a modern birthstone for November.

Coral  Rebekka Notkin 

Coral

Alternative Wedding anniversary: 35th

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Coral has been used in jewellery and carvings for centuries. It is an organic gem made from the external skeleton of tiny sea creatures called coral polyps. Corals form over generations and can grow to create vast underwater forests. Red to pink coral is the most valuable, with most being harvested in the Mediterranean Sea. Worldwide coral beds are severely depleted and as coral is vital to marine eco-systems, this coral is protected in many countries.

DIAMOND  (Ntinga) 

Diamond

Birthstone: April

Star Sign: Aries

Wedding Anniversary: 60th

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For a comprehensive guide to all things diamond, please visit our Diamond Buying Guide.

Pink Diamond  Sarah Ho

Coloured Diamond

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Although diamonds are traditionally more desirable when colour is absent, diamonds with intense colour are equally sought after. Red is amongst the rarest colours found in diamonds, along with blue and violet, but they come in almost every colour and shade. The most common colours are yellow and brown. Yellow colouration is due to nitrogen atoms scattered throughout the diamond. As the number of atoms increases, so does the depth of colour. Browns, pinks and reds are not caused by impurities but by physical forces squeezing and squashing the gemstone as it grew in the ground. This constant pressure causes the diamond structure to become distorted, resulting in these plastic deformations.

There are rare colour changing diamonds known as chameleon diamonds. These gemstones change their colour from green to brown if heated or left in the dark. When they return to their normal temperature or light, so does its colour. How this phenomenon occurs is still up for debate.

Emerald (Tivon) 

Emerald

Birthstone: May

Star Sign: Taurus

Wedding Anniversary: 35th and 55th

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A member of the beryl family of gemstones, emeralds appears in a variety of shades of green. Most commercial emeralds are a vivid deep green. The cause of the colour is due to the presence of chromium- the same element that causes rubies to be red. In their natural form, emeralds grow as large elongated hexagonal crystals and can be found worldwide. However, the best examples are thought to come from Colombia.

When purchasing an emerald, it is best to look for one that allows as much light in as possible. Perfectly clean emeralds are exceptionally rare, with most exhibiting a range of inclusions. However, a well-cut emerald can usually hide these natural inclusions and imperfections. These inclusions are knowns as the 'jardin' of the stone as they resemble foliage within the emerald. These inclusions can often be stunning, but they make the stones harder to cut than other gemstones. The emerald cut was developed to emphasise its colour and help protect the stone during the cutting process and avoid chipping during setting.

Emeralds, which are among the rarest and most valuable gemstones, are cut and measured in millimetres from length to width and not carat like a diamond. Colour is the most important factor when valuing and buying an emerald and are graded based on its hue, tone and saturation of colour. Hue refers to the emerald's physical colour, tone the depth of colour and saturation as the distribution of the colour.

249 Garnet Ruppenthal

Garnet

Birthstone: January

Star Sign: Capricorn

Wedding Anniversary: 2nd

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Unlike other gemstones on this list, garnets are not a single gem but rather a family of gems related by chemical make-up. Red and brown garnets are the most common commercial examples, but the gemstone can come in various shades and colours. Garnets have been used in jewellery for centuries, by Roman leaders and famed jewellers such as Fabergé. Today, garnets are often seen as outdated despite their beauty. Often seen in antique and vintage jewellery, red garnets (almandine) look equally beautiful set in contemporary pieces.

Red garnets are readily available, making them one of the most affordable gemstones on the market. Green garnets command higher prices due to their relative rareness. The most valuable garnet is the demantoid garnet, named for its high lustre (derived from adamantine, a diamond's lustre). Its unique inclusions appear in the form of radiating fibres known affectionately as horsetails.

Jade diamond earrings by Sarah Ho 

Jade

Birthstone: March

Wedding Anniversary: 12th

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Two different minerals are referred to as jade – jadeite and nephrite. Jadeite is harder on the Mohs scale, but nephrite jade tends to appear in large sizes. The imperial green colour synonymous with jade is only found in the jadeite variety, which tends to more expensive thanks to its vivid colour, translucence and rarity. Jade continues to rise in price and, as such, has resulted in an increase in imitations flooding the market. If looking to buy the real thing, make sure to see any laboratory reports that can verify the gemstone's quality.

 

Jasper

Birthstone: March

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Jasper is an opaque chalcedony that often appears in patterned varieties when used in jewellery. These multicoloured and patterned stones can be striking. Due to the abundance of jasper, these are inexpensive gemstones, with colour and distinctive patterns being the critical metrics for determining value.

 

Kunzite

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Kunzite is a beautiful but fragile gemstone and sought after by collectors. Kunzite appears in transparent pink to deep purple. Due to its delicate nature, it is hard to cut, meaning it is rare to find smaller stones and can fracture with small impacts. Unlike many gemstones, kunzite fades in sunlight.

Lapis Lazuli Karl Karter

Lapis Lazuli

Birthstone: September

Star Sign: Virgo

Wedding Anniversary: 9th

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Lapis lazuli is a combination of several materials. The blue colouration comes from lazurite, the white marbling effect from calcite and the golden fleck inclusions from pyrite's presence. Lapis lazuli has had a long history, having been mined for more than 6000 years. It is a stone of royalty and was used to inlay funeral masks of pharaohs such as Tutankhamun. The gemstone tends to be made into cabochons and beads, with its deep blue and gold flecks benefitting from a high polished finish.

Malachite Angel Whisperer   

Malachite

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Malachite gets its vivid green colouration from copper. Often exhibiting concentric bands of varying shades of green, malachite is an inexpensive and readily available gem. Due to its low hardness, it is easy to work with into jewellery and decorative objects. It is usually found in copper mines.

Moonstone (Ntinga)jpg

Moonstone

Birthstone: June

Star Sign: Gemini

Wedding Anniversary: 3rd

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Moonstone possesses a beautiful iridescence. This shimmering and ethereal appearance, known as adularescence, makes it a popular gemstone. Moonstones with a bluer adularescence command higher prices but white varieties are the most common commercial examples. Moonstones typically appear as cabochons.

Onyx  Harsh and Sweet 

Onyx

Wedding Anniversary: 7th

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Onyx is a type of chalcedony with layers of black and white colouration. This parallel coloured banding allows skilled carvers to cut away material to create stunning cameos with striking contrasts. Onyx can be cut into faceted jewels and was once popular as mourning jewellery due to its rich black colour.

Opal (Ntinga) 2 

Opal

Birthstone: October

Star Sign: Libra

Wedding Anniversary: 14th

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Opals are made from mineraloid, a form of silica. They are softer than many other gemstones. Many are made into cabochons as the curved surface helps the stone survive scratches and knocks to avoid damage. Although white or milky opals are the most common type found in jewellery, the gemstone can appear in all colours, shades and plays of colour.

Most commercial opals are untreated. It is important that inclusions in white opals are not evident to the naked eye. Opal size can be expressed either in carat weight or millimetres. Australia is responsible for the majority of the world's production of precious opal.

thumbnail Peridot GF Williams

Peridot

Birthstone: August

Star Sign: Leo

Wedding Anniversary: 16th

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Peridot is only found in green due to the presence of iron trace elements. It is sometimes known as an extraterrestrial gemstone as it is often discovered in meteor craters. It is, in fact, located all over the world in lava deposits and the earth's upper mantle. The most valued colour of peridot is a rich green but can be found in various shades, with the familiar yellow-green gemstone being the most commonly mined.

Peridot is a relatively inexpensive gem and is best to buy natural and untreated gemstones. It is still common to find heat-treated commercial peridot to intensify the colour. Peridot exhibits 'high double refraction - which is a clear double image of its pavilion facets. Inclusions in peridot may be present, but they must only be detected under magnification. Peridot exhibiting inclusions visible with the naked eye are best avoided.

Tahitian Pearls Ruppenthal

Pearl

Birthstone: June

Star Sign: Gemini

Wedding Anniversary: 1st and 30th

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Pearls are organic gems formed inside molluscs. When a grain of sand or other tiny object gets inside a mollusc's shell, a substance called nacre forms, covering the item and protecting the mollusc. Over time, more nacre forms and creates the pearl. As is more common today, these pearls can be cultivated by inserting an object inside a mollusc.

Pearls were historically a sign of great wealth. It was only in the early 20th Century when pearls became affordable due to pearl cultivation patented by Kokichi Mikimoto. Pearls are much softer than most traditional gemstones and can be easily scratched and damaged.

There are three types of pearl:

Natural Pearls – these are pearls that grow naturally, at random, inside either oysters or mussels. In the old days, all pearls were natural, but today such pearls are extremely rare and expensive and are not generally available.

Cultured Pearls – produced in oysters or mussels but with the intervention of people who introduce a foreign body or 'nucleus' into the creature, which it then covers in nacre or mother of pearl. Cultured pearls can be grown in sea or freshwater. Farmed freshwater pearls are more affordable than cultivated seawater pearls. This is because freshwater molluscs can produce more pearls at a time.

Synthetic Pearls – these are 'pearly' beads that are entirely man-made and are not pearls at all.

Types of cultured pearl:

  • Akoya - The original cultured pearl from Japan. Sizes are relatively small, 2-10mm and colours tend to be pale – cream, white/pink and silver.
  • South Sea - These valuable pearls from Australia, Indonesia and the Philippines are larger 10-22mm and range in colour from silvery white and cream to champagne and gold.
  • Tahitian - Tahitian pearls from French Polynesia and the Cook Islands are naturally dark; colours include black/green, aubergines and violet, as well as browns and gold. Sizes are 8 – 18mm.
  • Freshwater - These generally nucleus-free cultured pearls are mainly from China. They come in many different shapes and sizes and in colours from white, peaches, pinks and lavender. Sizes 2 -16mm or larger depending on the variety.
  • Keshi - Irregularly shaped 'blobs' of pearl that resemble hot metal dropped into water – Keshi can measure up to 20mm across.

The quality of a pearl depends on five criteria:

  • Lustre - This refers to the sheen of pearls. A good pearl should be deeply lustrous – the deeper the coating of nacre, the better the lustre will be. An iridescent pearl is most sought after.
  • Texture - Good pearls should ideally be flawless without any blemishes or hollows.
  • Shapes - Pearls can be many different shapes, but the most common are button, drop, round, oval and baroque (or irregular). The shape does not influence quality, but perfect examples of each shape are more highly prized, but this is a matter of taste.
  • Size - The size of a pearl is measured in millimetres and tends to depend upon the size of the original nucleus and the time the pearl has had to develop.
  • Colour - Colour is a matter of fashion and personal choice. Deeper colours, especially browns and greens, are currently popular.

Matching pearls within a piece of jewellery is desirable. Skilled jewellers will make sure individual pearls within a jewellery piece closely match each other based on the five criteria above. It is best to avoid purchasing treated pearls and avoid buying fakes. Make sure to buy from a reputable jeweller, like those who are members of the National Association of Jewellers.

Rose Quartz London Road 

Quartz

Birthstone: January

Wedding Anniversary: 5th (Rose)

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Quartz is one of the most common minerals globally. It produces a variety of gemstones, such as amethyst and rose quartz. The best examples of rose quartz come from Brazil, but the gemstone can be found around the world. Most rose quartz possesses a translucent to opaque appearance. It can be cut into many shapes thanks to its hardness and being found in large crystal sizes.

Some examples show an asterism (a star-like effect on the surface) when a spotlight is directed on the stone. The gemstone is regularly cut in a cabochon to accentuate this beautiful feature. Fabergé used the gemstone in the creation of the Imperial eggs.

Rhodolite Manja 

Rhodolite 

Wedding Anniversary: 15th

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Rhodolites are reddish-purple garnets. They are an affordable option and often paired with other gemstones in jewellery. Most commercial rhodolite has no inclusions visible with the naked eye.

Ruby Ntinga

Ruby

Birthstone: July

Star Sign: Cancer

Wedding Anniversary: 40th

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The gemstone of love, rubies come from the corundum family of gemstones, just like sapphires. Rubies derive their colour from trace elements of chromium. They are one of the hardest and most durable gemstones on earth (only moissanite and diamond are tougher). They are mentioned in Sanskrit scriptures as the 'king of gemstones' and good quality rubies of more than 10ct are rare and valuable and can fetch higher prices than diamonds of the same size.

It is common for rubies to be heat-treated to enhance their colour. Colour is the most important factor in determining value and quality. This is judged by hue, tone and saturation. Hue refers to the ruby's physical colour, tone the depth of colour, and saturation as the distribution of the colour. Natural inclusions are common in commercial rubies. Perfectly clear rubies are therefore scarce and fetch a premium. The best examples are found in Myanmar and other Far Eastern countries like Sri Lanka and Thailand. Round rubies are the most popular shapes and commonly used in solitaire rings, earrings, and accent stones.

Sapphire (Tivon)

Sapphire

Birthstone: September

Star Sign: Virgo

Wedding Anniversary: 45th and 65th

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Sapphires are part of the corundum family of gemstones. They can be found all over the world, from Scotland to Australia. Sapphires are seen as one of the big four gemstones. Pure sapphire is totally colourless. The familiar rich blue colour most people associate with the gemstone is caused by the interaction between iron and titanium atoms within the structure. Like many gemstones, the sapphire appears in many colours and not just blue. The Padparadscha sapphire appears in a reddish hue of pink and orange and is particularly desirable to collectors.

Sapphire is the second most popular gemstone behind diamonds. The traditional blue sapphire is a symbol of truth and nobility and is regularly found in Royal Regalia. Like other gemstones from the corundum family, colour is the most critical factor in determining quality and value. Sapphires, like rubies, are judged by hue, tone and saturation to assess quality. Kashmir remains the most famous region for sapphires but is no longer mined there on a commercial basis.

Spinel (Tivon)

Spinel

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Until the rise of modern gemmology in the last Century, many spinel gemstones were wrongly classified as corundum (the family of gemstones consisting of sapphires and rubies). The Black Prince's ruby mounted at the Crown Jewels' centre is arguably the most famous example of this misclassification. These incorrect classifications earned spinel a bad reputation for many years, but this beautiful gemstone (which can be found in shades of red, pink, purple and blue) is now becoming more sought after, particularly as it is rarer than the likes of rubies. However, it still tends to have a lower market value than its red cousin.

Tanzanite (Tivon)

Tanzanite

Birthstone: December

Wedding Anniversary: 8th or 24th

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Tanzanite, a variety of zoisite, is a relatively new and expensive gemstone discovered in 1967 in a remote corner of Tanzania. The only known source is a 6km strip of land at the foot of Mount Kilimanjaro. Due to this, it is said to be a thousand times rarer than diamond. The gemstone varies in colour and intensity and can shift from blue to purple when viewed from different directions. Most mined crystals start with brown colouration. It is not until being heat-treated that the beautiful blue colour is revealed.

Most crystals are relatively small, meaning very few large tanzanite gemstones come to market, while those that do fetch a premium. Buying tanzanite with great clarity is essential. It is best to avoid gemstones with visible inclusions or a dull cloudy appearance. Due to its relative newness and rarity, tanzanite is a highly desirable gemstone with a price to match.

Blue Topaz  Ruppenthal

Topaz

Birthstone: December

Star Sign: Scorpio

Wedding Anniversary: 4th (Blue)

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Topaz naturally appears in many colours, with pink and Imperial topaz being amongst the rarest. It is an affordable option for a gemstone, and historically the gemstone has signified peace and healing. Blue is the most common commercial colour but is usually heat-treated to achieve vivid colouration. Topaz is a versatile gemstone and regularly found in larger crystals that can be fashioned into many different cuts and shapes.

Green Tourmaline  Tivon

Tourmaline

Birthstone: October

Star Sign: Libra

Wedding Anniversary: 8th and 10th (Green)

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Tourmaline remains a popular gemstone due to the wide range of colours available. The term tourmaline refers to a family of related minerals, each with its distinct properties. Green tourmaline is one of the most popular colours. They are a versatile stone appearing in many sizes, easy to cut and often affordable. Rarer examples include the Paraiba tourmaline, a relatively recent discovery and desired for its striking neon blue-green colour.

Turquoise  Pomegranate NAJ Gemstone buying guide

Turquoise

Birthstone: December

Star Sign: Sagittarius

Wedding Anniversary: 11th

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The only gemstone to have a colour named after it, turquoise possesses an intense sky blue colour. Colour saturation is the most important factor in determining value. Turquoise is mined all over the world and has remained a popular gemstone in jewellery for centuries. 

Blue Zircon   London Road 

Zircon

Birthstone: September

Wedding Anniversary: 4th

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Zircon comes in a range of colours, from brown to blue. Most blue zircons are heat-treated. Green is the rarest natural colour, but blue remains the most popular and expensive. Colourless zircon can make excellent diamond imitations when properly cut. 

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