Ruby is one of the four highest valued coloured gemstones. In fact, large rubies can fetch higher prices than the same size diamonds. This precious gemstone has been prized for centuries due to its excellent Mohs scale hardness of 9 and rich red hue.
Ruby Origin and Formation
The English name “ruby” comes from the Latin word “ruber”, meaning red. In the ancient Indian language of Sanskrit, ruby is called “ratnaraj”, which translates as “king of precious stones”.
Rubies are formed under immense pressure and intense heat under the earth’s surface for millions of years. They consist of corundum and aluminium. Heat and pressure turn these minerals into a liquid and they seep into cracks in rocks.
When the liquid cools it usually turns to colourless crystals. As the corundum mixes with other minerals, it can alter from colourless into red, pink, blue and yellow.
If the trace mineral is chromium then the corundum turns red and we get rubies. In case the trace element is iron or titanium it gives us blue coloured sapphires.
The most important sources of ruby include Myanmar, Thailand, Sri Lanka and Tanzania. Other significant sources are Australia, Brazil, India, Cambodia, Kenya, Nepal, Pakistan, The USA, Vietnam and Zimbabwe.
The colour is the most important quality factor of rubies. To figure out which ruby colour is the best, we need to consider three factors – the hue, the tone and the saturation.
The hue describes how red is the gemstone and if there are any hints of other colours such as blue, brown or yellow. As a rule, the redder the stone, the better.
The tone refers to how light or dark the gemstone is. The best rubies have a solid colour that is not too dark and not too light. When the colour of rubies is too light, they are classified as pink sapphires, but the line between pinkish red rubies and pink sapphires varies by region. Some mining areas consider pink sapphires to be ruby.
The saturation is the characteristic that defines if the gem has weak, vivid, strong or intense colouring. The most desirable colour is a strong pure red and red with a hint of blue. This vibrant red colour is also known as “pigeon’s blood” usually sourced in Burma.
It’s worth mentioning that some rubies also possess fluorescence, that causes them to glow in ultraviolet light.
Natural rubies typically display inclusions, which are part of the nature of these gemstones. In fact, natural ruby can be distinguished from synthetic one by its inclusions, as the latter tends to be eye-clean.
Natural rubies that are free from eye visible inclusions are still available. However, large eye clean gemstones are very rare and extremely valuable.
Ruby Cut & Shape
Rubies often have mixed cut, with brilliant-cut crowns and step-cut pavilions. The most popular ruby shapes are ovals and cushions. Other shapes such as round, triangular, emerald, marquise and pear are also available, however, these are difficult to find in larger sizes. As rubies of over one carat are relatively rare, the price greatly increases with size.