Gemstone Buying Guide

Did you know that the Ancient Greeks were using gemstones in jewellery as far back as 1600BC? From Ancient Egyptian bangles inlaid with turquoise, to ornate Victorian necklaces dripping with emeralds, our relationship with these precious stones is long and full of emotion.

Renowned for their beauty, gemstones come in all colours of the rainbow – brilliant red rubies, deep green emeralds, and ocean blue sapphires being just a few. Their rich colours and brilliant sheen make them popular choices for jewellery around the world.

In this guide, we cover everything you need to know about buying gemstones. First things first…

What is a Gemstone?

Gemstones, also known as jewels or fine gems, are usually classified as precious or semi-precious stones.

Natural vs Synthetic Gemstones

Gemstones can be formed via two mediums: naturally or synthetically.

As the name suggests, natural gemstones are formed in nature. Most begin life as unrefined mineral crystals in the earth’s crust. Once mined, they are processed and cut into the smooth, lustrous stones we know and love. Certain rocks (like obsidian) or non-mineral, organic materials (like amber) are often considered to be gemstones as well.

Synthetic stones are grown in laboratories. Although often stigmatised as ‘fake’ or ‘artificial’ gemstones, they have exactly the same chemical composition as natural stones; the only difference is that they are grown through technology. The laboratory process results in fewer inclusions and flaws. They are usually more affordable than natural stones.

Which Gemstone Should You Choose?

As the old saying goes, beauty is in the eye of the beholder! There is no ‘best’ gemstone, just the one that most suits your preference and complexion.

Some people love the sparkle of vibrant, transparent gems like emerald, while others prefer the boldness of opaque gems like onyx.

Your budget may influence what type of gemstone you buy. Depending on type, size, and quality, gemstones can cost from under a hundred to several thousand pounds. The metal in which the gemstone is set, such as gold, silver, or platinum, will also hugely affect its price.

At Forum Jewellers, we offer jewellery inlaid with a wide range of gemstones. From ultra-rare tanzanite to opalescent pearl, which is considered a gemstone even though it is not a mineral, you’re sure to find something that you will fall in love with.


The origins of birthstones can be traced back to biblical times. Many people like to celebrate a special month by purchasing birthstone jewellery, either for themselves or as a gift for a loved one.

The generally accepted list of stones for each month are:

January: Garnet
February: Amethyst
March: Aquamarine
April: Diamond
May: Emerald
June: Pearl
July: Ruby
August: Peridot
September: Sapphire
October: Opal
November: Topaz / Citrine
December: Tanzanite

If you would like to know more about the meaning behind each of these gemstones, read our complete guide to birthstones!

Why Are Some Types of Gemstone More Valuable Than Others?

Some types of gemstone are much more expensive than others.

For example, diamonds are high in value because they cost a lot to bring to market, there is a limited supply, and they are in high demand. Diamonds used in engagement rings became popular in the 1930s and are said to symbolise eternal love.

Trends also have an effect – in the Victorian era, ‘mourning jewellery’ became popular following the death of Queen Victoria’s husband Prince Albert. Black gems like jet and onyx rose in price because of their use in mourning jewellery. Pearls are also worn traditionally during mourning and you will have seen ladies of the Royal Family wearing pearls when Queen Elizabeth II died.

Some gemstones, such as chrysoberyl, are rare but low in demand, making them cheaper than gems like ruby and emerald. Other factors that influence value include beauty and hardness (resistance to scratches).

How Do You Determine a Gemstone?

When valuing a gemstone, appraisers typically look at size, colour, clarity, and cut. Other qualities depend on the specific type of gemstone.


This rule is simple: the bigger the gem, the more it’s usually worth! The size of a gem is generally measured by weight in metric carats; one carat is equal to 1/5th of a gram or 200 milligrams (0.20 grams).

That said, if a smaller gem demonstrates exceptional colour or clarity, it may be more valuable than a larger gem with less impressive qualities.


Each type of gemstone has its own grading scale for colour. For example, the most valued sapphires are a pure, rich royal blue. Less valued sapphires are darker and more opaque. Gemstones are more valuable depending on how close they are to the market standard.

The most important aspects to consider are:

 Saturation (how intense the colour is)
 Tone (lightness)
Hue position (where on the RGB colour scale chart it is)


The clarity of a gemstone refers to its degree of transparency and how many inclusions and flaws it contains.

“Eye-clean” natural gemstones – those with no inclusions visible to the naked eye – are usually the most valued. An inclusion is any material that is trapped inside of another mineral while that mineral forms. However, some inclusions may actually increase the value of some gems. They may deflect light throughout the stone, improving colour uniformity, or simply add a sense of uniqueness.


The ‘cut’ of a stone does not refer to its shape; it refers to how well the proportion of the cut enhances the natural beauty of the stone. Due to the many variations involved, it is one of the most difficult qualities for non-professionals to evaluate.

Appraisers typically look at the following in a gemstone:

Windowing (when light passes straight through the center, rather than being reflected.)
Facet quality

It’s much easier to determine the quality of a cut under strong magnification.

Getting Your Gemstone Jewellery Appraised

Gemstone appraisal is a hugely complex process, and it takes many years of practice and training to become an expert. For the most accurate valuations, it may be worth consulting an appraiser.

An appraisal will also record important details for insurance purposes, should your gemstone be lost or stolen.

At Forum Jewellers, we offer a professional jewellery valuation service. We are a trusted Institute Registered Valuer and will use our years of experience to expertly identify the exact value of your jewellery. Get peace of mind by protecting your treasured assets!