For those born in September, sapphire is their birthstone. Here, Gem-A tutor Lily Faber FGA DGA EG, shares with us the history of this regal gemstone.
The word sapphire originates from the Greek word sappheiros, meaning “blue stone”. Sapphires are traditionally associated with the colour blue but they can come in any colour aside from red (which would be a ruby). One of the most valuable colours of sapphire is a natural, untreated padparadscha (orangey pink), meaning “lotus flower” in Sinhalese.
Sapphire with Fingerprint Feather Inclusion.Image Credit: Pat Daly.
Sapphires have always been prized for their colour and are believed by some to bring the wearer wisdom and truth. They can also allegedly attract divine favour, prevent the wearer from suffering envy, promote serenity and give one peace of mind. Often used in engagement rings, sapphires are a symbol of fidelity.
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Crystals and Inclusions
Sapphires can be found as either well-defined crystals or water-worn pebbles, depending on the type of gem deposit. If well-formed, they will take the shape of a hexagonal bipyramid or hexagonal barrel-shape with striations running horizontally across the crystal faces. They are often colour-zoned across the crystal or with hexagonal zoning in their cores.
Sapphire Crystal, makrs on crystal face from Mica. Image Credit: Pat Daly.
Inclusions are numerous and varied. A few include silk, zircon haloes (circular stress cracks around a zircon crystal), hexagonal and straight colour zoning, feathers (partially healed fractures), negative crystals, two-phase inclusions of a gas and liquid, and fingerprints, which are especially neat feathers.
Angular Colour-Zoning and Feather Inclusions in Sapphire. Image Credit Pat Daly.
Like star rubies, sapphires can display asterism due to silk inclusions running in three directions at 120 degrees to one another, and they can come in any colour. One of the most famous star sapphires is the greyish-blue Star of India, housed in the American Museum of Natural History in New York, NY, USA. It weighs 563.35 carats and displays a star on both the top and bottom of the stone, which is unusual for star sapphires.
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Most sapphires on the market today have been heat treated to promote that beautiful rich, blue colour. Starting life as a pale blue or milky white geuda sapphire, these stones are then heated to alter the colour to a more desirable hue.
Treated Sapphire, Glass Filled and heated. Three Stages: Geuda, Rough and Cut.
Image Credit: ©Gem-A, Pat Daly.
Another treatment is surface diffusion, which is achieved by heating an already faceted stone in colouring elements, such as iron and titanium, to produce a stronger blue colour that is surface-deep. The stone is then re-polished to sharpen the facet edges. One way to discover this treatment is to place the stone over a diffused white light either directly on the light or immersed in a liquid such as water or baby oil, and to look at the colour concentration.
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If the colour is mainly concentrated at the facet edges and you can see a clear girdle outline of the stone, it has been surface diffusion treated. If the girdle of the stone fades away and the colour zoning does not seem to be dictated by its relation to the facet edges, then it has not been surface diffusion treated.
Care and Caution
Sapphires have a hardness of 9 on the Mohs scale of hardness, and their ability to resist scratching and wear while taking a bright vitreous polish, not to mention their irrefutable beauty, makes them ideal for everyday wear. For good practice, do not put these gemstones in ultrasonic cleaners and be careful when setting them as they can chip or fracture.
While blue is arguably the most well-known and most popular of sapphire colours, it is a versatile gemstone because it can be found in a veritable rainbow of hues, and is well-suited as September’s birth stone.
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Cover image: Rutile Inclusion in Sapphire. Image Credit: Pat Daly.
Did you think this might be emerald? You certainly wouldn't be the first to confuse the vibrant green of dioptase with the more recognisable, jewellery-lover's gemstone. Here, Gem-A assistant gemmology tutor, Dr Juliette Hibou FGA, explains more about the history, properties and origins of dioptase, an unusual collector's gem.