Buying Gemstones

Gemstone

A rare beauty

Gemstones are rare due to having been created deep in the earth’s core through heat and stress over many, many millions of years. They are found in the harshest of places on earth from emeralds in the steaming heat of Colombia to diamonds in the baking sun of southern Africa.

The stones and their colours

With gemstones, the array of colours is virtually limitless. Let's explore each gemstone:

Diamonds

The ‘Prince of Gems’. Diamonds are the ultimate stone. Hard, durable, beautiful and with an unmatched sparkle.

Rubies and sapphires

The wonder of rubies and sapphires is they can be tailored to taste. They offer a range of beautiful blues or ravishing reds yet there are yellow, pink and violet sapphires, too.

Emeralds

The emerald’s green is intense yet it’s a brittle, more fragile stone. Which is why the emerald-cut shape was developed to protect it.

Tanzanites

Found only in Tanzania, the tanzanite marries purples and blues. Tender and tantalising.

Garnets

A rainbow of colours - red, marmalade orange and the intense green of tsavorite. Garnets are generally un-treated and more affordable.

Amethysts

Radiant in its shades of purple, legend has it that this durable member of the quartz family can protect against drunkenness!

Citrine

Citrine is a quartz, the pale yellow to brownish-orange cousin of amethyst. Its attractive colour, durability and affordability makes it the favourite yellow-orange gem.

Pearls

Pearls are a delicate, natural, organic mineral, beautiful and shimmering with a shiny lustre created by the mollusc host where they are grown. They are best worn or stored well away from other stones.

Topaz

From pinks to oranges, topaz comes in an explosion of colour, the most famous being sky blue.

Opals

Opals are unique for their sheer play of colour. As cabochons, the curved surface helps this less durable stone survive knocks and scrapes.

Peridots

Peridot is a uniquely apple green vitreous stone. The play of greens and small black inclusions surrounded by a halo give it its affectionate name of ‘Lily Pad’.

Aquamarines

As the name suggests, aquamarines were once thought to come from the sea, but the actually belong to the emerald family. Their long parallel-needle inclusions are colloquially known as ‘rain’!

Tourmalines

Tourmaline comes in green, blue-green, mint, yellow and even dusky pink.

Until relatively recently coloured gemstones were divided into two categories – precious and semi-precious – but as some ‘semi-precious’ stones are extremely rare and expensive this distinction has been abandoned in favour of simply ‘gemstones’. That said, some gemstones do command much higher prices than others and 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 to determine the quality of the stone you are buying in terms of its colour, cut and clarity. The report will also identify any treatments which may have been applied to the gemstone.

Gemstone treatments

In their cutting and polishing, 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 and is often combined with diffusion treatments designed to actually fuse colour into the surface of the gemstone. Irradiation is sometimes used to enhance the colour of gemstones such as topaz, tourmaline and fancy diamonds. Generally, these treatments are permanent.

Surface cavities which would otherwise reduce the value of a gemstone 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 intensity of the natural colour. 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.

A good gemstone laboratory will look for the signs of these treatments and include the information on the gemstone report. Some of these treatments can be controversial – they enhance the beauty of gemstones which otherwise might not be suitable for jewellery and bring them within the reach of consumers who otherwise might not be able to afford them. In some categories, it is difficult to find natural untreated gemstones, which can attract a significant premium.

Tanzanite, a variety of zoisite, is a relatively new and expensive gemstone, having been 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. This blue-violet gemstone varies in colour and intensity and recently a colour grading system was introduced to help. It has its own 4C’s grading system with the deeper coloured stones being the most prized. For further information visit www.tanzanitefoundation.com or www.anchorcert.co.uk.

For more detailed information about individual gemstones, visit the International Colored Gemstone Association at www.gemstone.org/.

The choice of pearl jewellery, both in terms of design and in relation to the type, size and colour of pearls employed has never been greater.

Stone Guides

If you want some more information about particular gemstones then view the guides below:

Buying Pearls

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 and as the table below demonstrates there are many different types.
  • Synthetic Pearls – these are simply ‘pearly’ beads which are entirely man-made and are not really ‘pearls’ at all.

Types Of Cultured Pearl

  • Akoya - The original cultured pearl from Japan. Sizes are relatively small, 2-10 mm 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 20 mm across.

Pearl Quality

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.
  • 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.