The buyer's guide to jewellery with coloured gemstones

They have inherent qualities of hardness, durability, rarity, lustre and sparkle.

Cut and polished, they have been used for millennia in the manufacture of jewellery, objects of personal adornment and works of art. From agate to zoisite, there are myriad varieties.

Typically, gemstones are grouped according to chemical composition rather than simply colour. Sapphires, a variety of the mineral corundum, come in yellow, pink and a pinkish orange called padparadscha as well as blue.

Tourmalines come in many varieties and colours including pink, yellow, orange, purple and blue while garnets typically associated with a deep red hue, can also be found in many lighter shades and in both orange and green.

All gemstones come in a range of quality. Every mine will produce stones of different grades – some of them gemstone quality but others displaying the imperfections or shortfalls in colour that reduce their intrinsic value. A huge range of material, from ‘best in class’ stones to more affordable jewels, is available at auctions on thesaleroom.com every week.

What to look for

Just as with diamonds the big three ‘precious’ coloured gemstones (emeralds, rubies and sapphires) are graded using the traditional criteria of the four Cs, namely colour, cut, clarity and carat weight.

Coloured stones are often described in terms of hue, saturation and tone. A professional gemmological report will reference these while providing the geographical origin of the stone – a significant factor in the value of many premium coloured gemstones.

This pair of cabochon emerald and ruby spray earrings, c.1940, sold at £320 at Sworders on June 2022.

Rubies for example, which command the highest price per carat of all gemstones (except for coloured diamonds) are found in many geographical locations but it is the stones from Burma, admired for their saturated colour and a natural fluorescence caused by a high chromium content in the ground from which they are extracted, that are considered the best.

Good quality sapphires are found in Burma, Sri Lanka, and Madagascar but it is the vivid blue stones from the Kashmir mines – a source active for just five years in the late 19th century – that command the greatest premium.

A gemmologist will also look for evidence of heat or chemical treatment (often used to enhance or change the colour of a stone) or stones created by wholly synthetic means.

Pearls, for example, are measured according to size, shape and lustre. However, the key ingredient in value is whether the pearl has grown naturally in warm saltwater or was simply farmed.

Most gemstones offered at auction won’t come with a technical report but they should have an indication of their inherent qualities in the catalogue entries. Always read the lot description carefully before bidding and feel free to contact the auction house to request more information. Many auctioneers will employ a qualified gemmologist.

Importance of rarity

Some exceptions aside, there exists an established hierarchy in the pricing of gemstones, based primarily on rarity. Many of the ‘secondary' gemstones are found in much larger sizes and weights and therefore prices are less sensitive to the number of carats.

A 10ct gemstone quality ruby is a geological miracle. Similar-sized specimens of ‘semi-precious’ stones such as amethyst, topaz or aquamarine are not unusual.

Other gemstones such as coral, amber, jade or turquoise, tourmaline are typically only termed ‘fine or ornamental’ with just the very best examples deemed of gemstone quality. Here the value of a piece of jewellery will typically lie in its age, workmanship, setting and decorative appeal rather than any great intrinsic value in the stones themselves.

Birthstones

Some buyers like to search for their ‘birthstone’ – a different gem for each of the months of the year. Here is a list of each birthstone by month:

January – garnet

February – amethyst

March – aquamarine

April – diamond

May – emerald

June – pearl or alexandrite

July – ruby

August – peridot

September – sapphire

October – tourmaline or Opal

November – topaz or citrine

December – tanzanite or turquoise

Hardwearing stones

An important thing to consider when buying jewellery with gemstones is how often you’re likely to wear the piece. One reason diamonds are so popular for engagement rings is due to their hardness and durability.

Earrings with oval cabochon emerald within a border of oval cabochon rubies and round brilliant cut diamonds, in yellow and white claw settings. The pair sold for £900 at Tennants in July 2022.

However, hardwearing gemstones like sapphires, rubies and tourmaline are also very suitable for everyday wear and make a great alternative for an engagement ring. These items are likely to keep in good condition, survive any knocks and stand the test of time.

Jewellery featuring less hardwearing stones like emerald and opal are better suited for pieces worn primarily for special occasions as they’re slightly less able to withstand the wear of daily use.

What to do next

Decide how much you’d like to spend and use the search facility on thesaleroom.com to find gemstones coming up for sale.

You can filter your search by, among other things, price and by location of the auction house to narrow down your selection.

To research recent prices at auction to see how much different types of gemstones sold for you can also try out thesaleroom.com’s Price Guide.

If you are new to bidding check out our guides to buying at auction – it’s easy once you know how.