Gemstone Education: Understanding Gemstone Quality
Understanding gemstone quality
When evaluating gemstones, several characteristics are used to determine their beauty and value. Similar to diamonds, gemstones are assessed based on a combination of visual qualities and natural characteristics.
Key factors that influence a gemstone’s quality include colour, clarity, cut and size.
Colour in gemstones
Colour is often the most important characteristic when assessing a gemstone. The beauty and value of many gemstones are primarily determined by their colour.
Gemstone colour is usually described using three components:
Hue – the dominant colour of the gemstone, such as blue, red or green.
Tone – how light or dark the gemstone appears.
Saturation – the intensity or strength of the colour.
In many gemstones, stones with strong, vibrant colour and medium tone are considered the most desirable. Colour, followed closely by transparency, plays a major role in determining a gemstone’s value.
Gemstone clarity
Most gemstones contain natural inclusions, which are internal characteristics formed during the gemstone’s natural growth.
These inclusions are completely natural and contribute to the individuality of each stone. Some gemstones, such as aquamarine, typically contain very few inclusions, while others, such as emerald, naturally contain many.
Clarity affects how transparent a gemstone appears. A large number of inclusions can reduce transparency, which may influence both the visual appeal and the value of the stone.
Gemstone cut
The cut of a gemstone refers to how it has been shaped and polished from the original rough crystal.
A well-cut gemstone should reflect light evenly, highlight the gemstone’s natural colour and display good symmetry and proportions.
Proper cutting helps maximise the beauty of the gemstone and ensures the colour and brilliance are presented at their best.
Gemstone size
Unlike diamonds, a gemstone’s carat weight does not always accurately represent its visual size.
Different gemstones have different densities, meaning two gemstones that appear similar in size may weigh different amounts.
For this reason, gemstones are often described using their physical dimensions, such as 6 mm × 4 mm or 7 mm × 5 mm, rather than carat weight alone.
Sapphire and Ruby
Sapphires and rubies belong to the corundum mineral family and have a hardness rating of 9 on the Mohs scale. This makes them among the hardest gemstones available and suitable for jewellery that is worn regularly.
Although sapphires are most commonly associated with blue gemstones, they can occur in a variety of shades including pink, orange, yellow and brown.
Rubies occur in different shades of red, ranging from deep red tones to lighter pinkish hues. Colour plays the most significant role when evaluating rubies, with stronger and more vivid colours generally being more valuable.
Sapphires and rubies are mined in several regions around the world, including Sri Lanka, Thailand, India, Myanmar and Australia.
These gemstones almost always contain natural inclusions, which are a normal and expected part of their formation.
Treatments used for sapphires and rubies
The vast majority of sapphires and rubies available today have undergone heat treatment. In fact, more than 95% of these gemstones are treated in this way.
Heat treatment is widely accepted within the jewellery industry and is used to improve the gemstone’s colour and overall appearance.
Other treatments such as fracture filling, dyeing or chemical treatments are not widely accepted within the industry.
Emerald
Emeralds belong to the beryl mineral family and have a hardness rating of 7.5–8 on the Mohs scale.
Although this hardness is relatively high, emeralds are considered to have moderate durability due to their internal structure. As a result, they are often recommended for jewellery that is worn with a little more care.
Emeralds are known for containing a significant number of inclusions. These inclusions are often visible and contribute to each stone’s individual character.
Because emeralds frequently contain surface-reaching fissures, many are treated with oils to improve clarity. This is a common and widely accepted practice within the gemstone industry.
However, other treatments such as the use of resins, glass or synthetic polymers are generally not accepted.
Emerald colour can vary from lighter green tones to deeper shades. The most valuable emeralds typically display a rich green to bluish-green appearance.
Due to their structure, emeralds should be cleaned carefully. Cleaning methods that involve high heat, steam or harsh chemicals should be avoided.
