Everyone knows the most famous and desired gemstone in the world is a diamond. It’s a combination of brilliance, fire (dispersion) and lustre make a diamond unique amongst gemstones. It’s uniquely hard, transparent and, of course, shiny. It’s these characteristics that have earnt diamond the reputation as the perfect gemstone.
While diamond has firmly established its place as the king of gemstones there are three other stones which are considered precious gems: ruby, sapphire and emerald, all other gem-quality stones are considered semi-precious. With the recent introduction of our ‘fine gems’ collection to our website, we thought it an appropriate time to further explore ruby, sapphire and emerald; what about them makes them precious and how to identify high-quality variations of the stones.
It is a surprise to many to learn that, chemically speaking, ruby and sapphire are brother and sister. They are both crystal forms of the mineral corundum, which in its pure form is colourless. However, it usually contains traces of certain elements that produce a wide range of colours. Traces of chromium produce a red colour and are named ruby, while stones of all other colours are referred to as sapphire.
The strength of ruby’s red depends on how much chromium is present – the more chromium, the stronger the shade of red. Chromium can also cause fluorescence, which adds to the intensity of the red colour. ‘Pigeons’ blood’ is the name given to the colour that every ruby aspires to: the perfect balance of red that is caused by minute traces of chromium (only a few parts per million) and is not too purple or blue, but not too orange or pink either. For the last 800 years or so the most important source has been Burma, and more specifically the famous stone in the Mogok Valley.
Sapphire, on the other hand, contains minute traces of iron and titanium to cause the colour blue. In a similar way, the more iron the corundum contains, the darker the blue. While the finest sapphires in the world are usually from Kashmir, India, there are other localities which produce high-quality sapphires too. Burmese stones are normally of a deeper, richer, more intense hue sometimes called ‘royal blue’. Their Ceylon or Sri Lankan counterparts, by contrast, tend towards paler, brighter colours. The most famous sapphire in the world is the 12 carats oval Ceylon sapphire featured as the centre stone of the engagement ring of Katherine Middleton and Prince William – previously worn by Princess Diana.
The third and final gemstone which is considered precious is emerald. Emeralds were first mined as long as 3,500 years ago at the legendary Cleopatra mines. These early emeralds were mainly low quality with poor transparency and a much paler green than what we see today. In the early 16th century, the Spanish first introduced Colombian emeralds to the world. Today, emeralds are found in other localities including Brazil, Zambia, Afghanistan and Pakistan but it is still Columbia that is considered as having the highest quality emeralds. The reason for this is that Colombian emerald deposits are the only ones on earth found in sedimentary host rock rather than in Igneous rock and therefore they are considered the purest in the world.
Top pedigree emeralds are always in demand, particularly the best material from Colombia, and geologists estimate that are emeralds are 20 times rarer than white diamonds. This is partly due to their hazardous formation process. Such a formation process means that emerald is often found in relatively small pieces and even the best examples often have visible inclusions, internal fissures and fractures, which are sometimes referred to as the Jardin of a stone.