Last updated on December 12, 2023
Sapphire is one of the four recognized precious gemstones and the second hardest mineral on earth after diamond. The birthstone of September, this deep blue gemstone has been adored for its colour, durability and beauty since ancient times.
Sapphire Origin and Formation
The name sapphire comes from the Greek word “sappheiros” or the Latin word “saphirus”, both of which mean “blue”. Like diamonds, sapphires take millions of years to form, and no two natural sapphires will ever look the same. They are formed beneath the earth’s surface under immense pressure and intense heat out of the mineral called corundum (aluminium oxide) which seeps into cracks in igneous or metamorphic rocks. Once the liquid cools, it turns into colourless crystals. However, when minuscule traces of other minerals (often as little as 1%) mix with corundum, they turn it into various colours such as red, pink, blue, yellow, etc.
If the transition microelement is iron or titanium, the corundum turns blue, and we get blue sapphires. In the case of chromium, the corundum turns red and gives us rubies. The other sapphire colours are caused by various mixes and proportions of iron, titanium and chromium.
Most corundum in nature is heavily included and suitable only for industrial use, while gem-quality corundum is very rare. Rough sapphires come in a barrel shape, tapered at the ends and larger in the centre. Once mined, they can be cut into any shape and used for jewellery manufacturing.
Sapphire deposits can be found in Madagascar, Sri Lanka, Myanmar, Thailand, China, Australia, Nigeria, Pakistan, Kashmir, Nepal and the United States. Depending on the location they come from, sapphires can have different chemical properties and inclusions. Gemstones from Kashmir, Burma and Sri Lanka are the most prized due to their high quality and clarity.
When corundum takes on a colour other than red, the gemstone is typically classified as sapphire, meaning there are many colour varieties in sapphires. While the “official” colour of this gemstone is blue, the other colours such as pink, purple, green, orange and yellow are sometimes referred to as “fancy sapphires”. However, this term does not apply to the colourless, black and blue specimens.
When iron is present in the chemical composition, the sapphire takes on a yellow colour. While vanadium sapphires get purple, the best-known blue sapphires are created if iron or titanium is present in their structure. Burmese and Kashmir sapphires usually have an intense and velvety blue colour; however, these stones are very rare nowadays. Today the most common sapphires are the ones from Sri Lanka and Madagascar, which come in light to dark blue colours.
In general, the intensity of blue is the most important factor with blue sapphires, meaning a big stone with a washed-out blue colour will always cost less than a small vivid blue stone. The most desirable sapphire colour is the intense cornflower blue which is not too dark. In general, stones that have too dark or too light colours are not that valuable. However, light blue stones have greater brilliance than darker ones. Another highly-priced and possibly the rarest specimen is the padparadscha sapphire, named after a delicately coloured lotus flower. It is a unique blend of pink and orange sapphire resulting in a stunning peachy or salmon colour.
There are also colour-change and bi-coloured sapphires, which are exceptionally rare. The ability to change colour when viewed under different types of light is a rare phenomenon in the world of gemstones. However, some sapphires display a bluish colour in daylight and a reddish colour under electric lights. Bi-coloured sapphires display two different colours under the same lighting conditions.
Although both sapphires and rubies are formed in a similar mineral structure, sapphires often have better clarity. They can come transparent to opaque, with transparent stones being the most valuable.
Sapphires can come with several types of inclusions such as needles (fine needles are called silk), mineral crystals, feathers, partially healed breaks that look like human fingerprints and colour zoning. Each of these inclusions has a different impact on the stone’s sparkle and light performance.
In general, inclusions make a sapphire less valuable. The price can drop significantly if the inclusions affect the stone’s durability. However, inclusions can also increase the value of some sapphires. The most valuable Kashmir sapphires contain tiny silk inclusions that give them a velvety appearance. The same silk causes phenomenal asterism in star sapphires. This effect is caused by reflections from needle-like inclusions oriented in specific directions, resulting in 4, 6 or 12 rays.
Sapphires are available in various cutting styles, with oval being one of the most popular shapes. The initial shape of the raw sapphire greatly influences the eventual shape and size of the polished gem. Since raw sapphires typically have a barrel-like form, the resulting stones often exhibit depth. To achieve optimal colour, and proportions and minimize weight loss, lapidaries must also pay attention to colour zoning—distinct areas within the stone displaying different hues. For instance, blue sapphires often feature zones of lighter and darker blue, necessitating precision in placing the richest colour in a way that it shines most brilliantly in the final gem.
A well-executed sapphire cut showcases remarkable brilliance and sparkle. As light enters the gem, it elegantly dances within, creating a vivid interplay of colours and flashes before exiting. The cut can either elevate or diminish these optical qualities. A precisely cut sapphire maximizes the dispersion of light, resulting in a mesmerizing visual spectacle.
Sapphire Carat Weight
Sapphires exhibit a wide range in size, spanning from just a few points to several hundreds of carats. Notably, larger blue sapphires are more commonly found than their ruby counterparts. However, it’s important to mention that the majority of commercially available sapphires typically weigh less than 5.00 carats. While large commercial-quality sapphires are relatively rare, they are more accessible than their fine-quality counterparts. Consequently, when it comes to fine-quality sapphires, size plays a pivotal role in determining their price. This rarity of larger, fine-quality sapphires underscores their allure and premium pricing within the gemstone market.
|Hexagonal and trigonal
|Blue, pink, purple, yellow, green, orange, colourless, grey, black and multicoloured
|9.00 on the Mohs scale
|1.76 - 1.77
|3.98 ~ 4.06
|Transparent to opaque
|Vitreous to adamantine
|None, but may exhibit parting
Featured image: photo-world / Shutterstock