What determines the value of a gemstone?

Have you ever thought about the price of the gem adorning your ring? The truth is that jewels do not have a universal pricelist: the price is determined by the demand in the market. There are countries that try to impose more regulations on the sector, but these only apply in this country. Internationally, only the factors to be considered in the pricing are agreed upon. Below we will give a brief overview of them.

Before we talk about the pricing of gemstones, let’s agree that this here only applies to gemstones used in jewellery, that is, precious and semi-precious stones. Tumbled semi-precious stones kept in your pocket and sold in bulk cannot be used in jewellery. Only the crystals and semi-precious stones valued as top-quality find their way to jewellery. 

Traditionally, diamond, ruby, sapphire and emerald are considered precious stones and these are also the most expensive gemstones. But the value of the rock does not always depend on its type. If the quality is low, also the price is low. The majority of the mines worldwide actually provide low-quality colourful gems and diamonds while the top-quality gemstones are found more rarely. In addition to the frequency of occurrence, also the country of origin, the colour, transparency and clarity of the rock as well as the cut and size (carat) are considered and also whether it has been processed or not.

But where should I start when determining the value of my ring? The most important thing is to determine the origin of the rock.

Natural or synthetic?

The first thing is to establish if your rock is natural or man-made. As the demand for gems and diamonds has increased rapidly, there are numerous synthetic gemstone analogues in the market that cannot be differentiated from the natural rock with a naked eye. For instance, instead of diamonds, relatively inexpensive natural or synthetic zircons are often used, but also moissanite which is a high-technology substitute for diamonds and rather expensive.

If you are not sure where the rock on your ring comes from and you have no certificate, you can always have it valued at the assay office or the jewellers. They will determine its type, whether it is natural or man-made and whether it has been processed or not. This is not enough to make the final judgement, but the first step has been made: we know what parameters need to be used in the evaluation. The next step is to determine four additional criteria: colour, clarity or transparency, quality of the cut and the weight or size.

The brighter, the better

Once you know what kind of a rock you have, you should find out how valuable the colour of your rock is. Each gemstone family has a colour that is considered the most valuable one. For instance, tourmaline can appear in various colours in nature, but the most precious ones are electric blue and deep pink, but also emerald green.

In addition to the hue, also the lightness or darkness and brightness of the colour are considered. The thumb rule is – the brighter the colour, the more expensive the rock. For instance, amethyst (in the necklace in the photo) is a rock whose price largely depends on the hue. The deeper and darker the purple, the more expensive, and in the most expensive amethysts, the light shimmers and refracts in blue and red hues. If amethyst is generally considered a semi-precious stone, then such expensive ones are definitely classified among precious stones.

People do not usually know that also diamonds can be found in nature in different hues. Most of these remain on the scale from colourless to light yellow or brown. The rarer and more expensive diamonds are chemically pure and perfect in structure with no hues whatsoever – they are like drops of pure water. Even the smallest differences in tone come to play a considerable role in the price and the differences are often so subtle that you cannot differentiate between them with a naked eye.

There are also black, red, green, blue and orange diamonds. The most precious ones are red, but actually all coloured diamonds are expensive as they are highly rare – constituting less than 1% of all diamonds in the world.

Transparency is important, but with exceptions

Nature is perfect, but it does not always mean perfect transparency. In case of transparent crystals, we presume that they lack inner nodules visible to the eye, bubbles etc. But the given assumption does not always apply as actually transparency is valued pursuant to the type of rock. For instance, if amethyst is presumably transparent, then it is extremely rare that we find a completely pure and transparent emerald. Perfectly pure and bright emerald can cost as much as a diamond, while a translucent or opaque emerald costs only around 30 euros, but they are nevertheless both emeralds. (The picture features a slightly translucent emerald.)

Some crystals seem to be full of cracks – it is perfectly normal in case of many rocks, for instance, the beautiful rutilated quartz or the sparkling Herkimer diamond. Much like all other gems, it applies also to diamonds. It may happen that some unwanted minerals or something else have been trapped in the diamond that come to affect its clarity and thus also the price. Entirely perfect diamonds are highly rare. It may happen that people who have worked with diamonds all their life have not even seen a sample of the diamond of the highest rank.

It is not possible to determine the clarity of a diamond with a naked eye. If you wish to know the clarity level of your diamond, you need to turn to specialists who can magnify it at least ten times.

The size is determined by weight

First try to establish how much the gemstone weighs. Gemstones are traditionally valued in carats: one carat equals 2/10 of a gram (0.2). Weight is the most important factor in case of diamonds – they are weighed up to a thousandth of a carat (0.001) and rounded up to the nearest hundredth or point. Each digit after the point can mean a price difference of hundreds or even thousands of euros depending on the quality of the diamond.

Many people probably find the weight and value ratio surprising. People know that a kilogram of sugar costs twice as much as half a kilogram, but gems and diamonds are not like sugar. Their price depends on several variables with weight being only one of them. The larger the diamond, the faster the growth in the price: if a one-carat diamond or gem is worth 6000 euros, then a two-carat diamond of similar quality can cost already 15,000 euros.

Similarly, also semi-precious stones are often priced according to their size – in case of two rocks of similar quality indicators, the larger one is always more expensive with the price increasing faster than the weight of the rock.

A good cut can increase the price, a bad one lower it

The way the gemstone is cut and polished plays a considerable role in its pricing. The cut can influence the sparkle and the colour of the gem as the hue and brightness are determined by the reflection of light from the stone.

It is usually said that the so-called diamond cut is more expensive and the so-called cabochon cut less expensive. The latter is cheaper primarily because it is much easier to do than a faceted cut. But in case of semi-precious gemstones, it can also be a sign of the rock quality – only high-quality gems can be given a faceted cut. Gemstones with uneven structure, inner cracks or nodules tend to shatter when given a faceted cut. 

All previous stones are given the kind of a cut that accentuates the rock’s positive features. Multicoloured tourmalines are often given a step cut to accentuate their hues. Emerald has its own step cut as it is relatively brittle and it is important to avoid excessive facets. The large pavilion under the gem makes the colour deeper while the cabochon cut may be the only option to show the inner light effects (cat’s eye or asterism) or the beautiful pattern (for instance, with a pietersite or fluorite in the jewellery).

But when talking about truly precious stones such as diamond, ruby, emerald or sapphire, it is not the shape of the crystal but the quality of the cut that matters. Here we consider the proportions and symmetry of the facets and the quality of the polishing. If the gem has a disproportionate cut, it will lose in its value.

The best way to evaluate the cut and sparkle of the gem is in daylight. A perfectly cut and polished diamond is dazzling. Each facet communicates with light, telling of the lapidary’s professionalism. A diamond’s amazing patterns of light are the result of internal and external reflections: there must be sufficient contrast between lighter and darker areas to make the pattern sharp. The lighter the hues, the higher the estimation given to the cut.

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Photo: Bryan Schneider from Pexels