Sapphire is one of the four recognized precious gemstones and the second hardest mineral on earth after diamond. This deep blue gemstone has been adored for its colour, durability and beauty since ancient times. Let’s see what makes it such a popular choice for any type of jewellery for such a long time.
Sapphire Origin and Formation
The name sapphire comes from the Greek word “sappheiros” or the Latin word “saphirus” which means blue.
Like diamonds, sapphires take millions of years to form. No two natural sapphires will ever look the same. Large natural sapphires are very rare, especially those that are not included. Rough sapphires come in a barrel shape that is tapered at the ends and larger in the centre. Once mined, they can be cut into any shape and used for jewellery manufacturing.
Sapphires are formed out of the material called corundum (aluminium oxide). Most corundum in nature is heavily included suitable only for industrial use, while gem-quality corundum is very rare.
Corundum gets colour if there are other minerals present while it is forming. Sapphires are typically found in recrystallized limestone and have a lot of aluminium in their crystal structure. Different transition metal minerals can change the white colour of sapphires into various colours such as yellow, orange, pink, green, purple and most popular blue.
In general, when corundum takes on a colour other than red, the gemstone is typically classified as sapphire.
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 quality and clarity.
As mentioned above there are many colour varieties in sapphires. The “official” colour of this gemstone is blue, while all other colours are referred to as “fancy sapphire”.
When iron present in the chemical composition, the sapphire takes on a yellow colour. When vanadium, sapphires get purple. And the best-known blue sapphires are created if iron or titanium is present in the structure.
Burmese and Kashmir sapphires usually have an intense and velvety blue colour, however, these stones are very rare nowadays.
The most common sapphires today are the ones from Sri Lanka and Madagascar that come from light to dark blue colour.
In general, the intensity of blue is the most important factor with blue sapphires. For example, a big stone that has a washed-out blue colour will always cost less than a small vivid blue stone.
The most desirable colour is the intense cornflower blue that is not too dark. In general, the stones that have too dark or too light colour are not that valuable. However, light blue stones have greater brilliance than darker ones.
Often sapphires have better clarity than rubies though both are formed in the similar mineral structure. Sapphires can come transparent to opaque. Transparent stones are 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.
In general, inclusions make a sapphire less valuable. Price can drop significantly if the inclusions affect the stone’s durability. However, 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 that are oriented in specific directions, resulting in 4, 6 or 12 rays.
Sapphires come in all cutting styles, the most popular shape being oval.
It’s worth mentioning that the shape of the sapphire rough has a great influence on the shape and size of the finished stone. Since rough sapphires usually come in barrel shape the finished stones are often deep.
To achieve the best overall colour, proportions and minimal weight loss, cutters also have to focus on such a factor as colour zoning (areas of different colours in a stone). For example, blue sapphires have zones of lighter and darker blue and cutters have to concentrate colour in a location that is best visible in the finished stone.
Sapphire Carat Weight
Sapphires come in size range from few points to hundreds of carats. However, the most popular sizes are less than 5 carats.
Fine-quality big stones are very expensive. For example, a 5-carat fine-quality blue sapphire can cost five times more per carat than the same quality 1 carat stone. This example is not meant to be an exact price guideline, but to illustrate how much the price-per-carat can go up as the quality and size rise.
Cover image credit: GIA